$MRSN
Mersana Therapeutics, Inc. Stock $mrsn

$mrsn Overview Financials Valuation SEC Filings Company Website

2021 Q4 Form 10-K Financial Statement

#000162828022004101 Filed on February 28, 2022

Income Statement

Concept	2021 Q4	2021	2020 Q4
Revenue	$11.00K	$43.00K	$10.00K
YoY Change	10.0%	-94.81%	-76.19%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin	$10.67M	$36.89M	$5.910M
YoY Change	80.61%	68.44%	40.38%
% of Gross Profit
Research & Development	$37.37M	$132.0M	$22.86M
YoY Change	63.48%	96.93%	83.89%
% of Gross Profit
Depreciation & Amortization	$211.0K	$855.0K	$260.0K
YoY Change	-18.85%	-15.35%	-10.34%
% of Gross Profit
Operating Expenses	$48.04M	$168.9M	$28.77M
YoY Change	66.97%	89.91%	72.89%
Operating Profit
YoY Change
Interest Expense	-$952.0K	$1.267M	$92.00K
YoY Change	-1134.78%	252.92%	5.75%
% of Operating Profit
Other Income/Expense, Net		-$1.202M	-$82.00K
YoY Change		-1949.23%	-123.16%
Pretax Income	-$48.98M	-$170.1M	-$28.84M
YoY Change	69.84%	93.14%	77.48%
Income Tax		$0.00
% Of Pretax Income
Net Earnings	-$48.98M	-$170.1M	-$28.84M
YoY Change	69.82%	93.15%	77.55%
Net Earnings / Revenue	-445300.0%	-395488.37%	-288440.0%
Basic Earnings Per Share		-$2.41	-$0.42
Diluted Earnings Per Share	-$680.9K	-$2.41	-$0.42
COMMON SHARES
Basic Shares Outstanding	71.91M shares	70.58M shares	68.50M shares
Diluted Shares Outstanding		70.58M shares

Balance Sheet

Concept	2021 Q4	2021	2020 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments	$177.9M	$177.9M	$255.1M
YoY Change	-30.24%	-30.24%	155.63%
Cash & Equivalents	$177.9M	$177.9M	$255.1M
Short-Term Investments			$0.00
Other Short-Term Assets	$10.95M	$10.95M	$3.500M
YoY Change	212.89%	212.89%	133.33%
Inventory
Prepaid Expenses
Receivables	$0.00
Other Receivables
Total Short-Term Assets	$188.9M	$188.9M	$258.6M
YoY Change	-26.95%	-26.95%	155.2%
LONG-TERM ASSETS
Property, Plant & Equipment	$1.968M	$14.86M	$1.730M
YoY Change	13.76%	16.98%	-20.06%
Goodwill
YoY Change
Intangibles
YoY Change
Long-Term Investments
YoY Change
Other Assets	$2.356M	$2.356M	$2.153M
YoY Change	9.43%	7.09%	48.18%
Total Long-Term Assets	$17.21M	$17.21M	$14.82M
YoY Change	16.15%	16.3%	138.44%
TOTAL ASSETS
Total Short-Term Assets	$188.9M	$188.9M	$258.6M
Total Long-Term Assets	$17.21M	$17.21M	$14.82M
Total Assets	$206.1M	$206.1M	$273.4M
YoY Change	-24.61%	-24.61%	154.23%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$12.32M	$12.32M	$8.340M
YoY Change	47.73%	48.45%	14.31%
Accrued Expenses	$28.72M	$31.02M	$16.15M
YoY Change	77.85%	76.24%	79.68%
Deferred Revenue	$3.944M		$3.987M
YoY Change	-1.08%		-17.2%
Short-Term Debt	$0.00	$0.00	$0.00
YoY Change
Long-Term Debt Due	$0.00	$239.0K	$0.00
YoY Change		139.0%	-100.0%
Total Short-Term Liabilities	$47.52M	$47.52M	$30.00M
YoY Change	58.39%	58.41%	24.65%
LONG-TERM LIABILITIES
Long-Term Debt	$24.63M	$25.08M	$4.977M
YoY Change	394.8%	382.21%	18.47%
Other Long-Term Liabilities	$974.0K	$11.77M	$174.0K
YoY Change	459.77%	15.41%	-36.73%
Total Long-Term Liabilities	$25.60M	$36.85M	$5.151M
YoY Change	396.99%	139.27%	15.08%
TOTAL LIABILITIES
Total Short-Term Liabilities	$47.52M	$47.52M	$30.00M
Total Long-Term Liabilities	$25.60M	$36.85M	$5.151M
Total Liabilities	$84.37M	$84.37M	$45.31M
YoY Change	86.2%	86.25%	55.06%
SHAREHOLDERS EQUITY
Retained Earnings	-$450.5M		-$280.4M
YoY Change	60.64%		45.77%
Common Stock	$572.2M		$508.5M
YoY Change	12.53%		87.87%
Preferred Stock
YoY Change
Treasury Stock (at cost)
YoY Change
Treasury Stock Shares
Shareholders Equity	$121.7M	$121.7M	$228.1M
YoY Change
Total Liabilities & Shareholders Equity	$206.1M	$206.1M	$273.4M
YoY Change	-24.61%	-24.61%	154.23%

Cashflow Statement

Concept	2021 Q4	2021	2020 Q4
OPERATING ACTIVITIES
Net Income	-$48.98M	-$170.1M	-$28.84M
YoY Change	69.82%	93.15%	77.55%
Depreciation, Depletion And Amortization	$211.0K	$855.0K	$260.0K
YoY Change	-18.85%	-15.35%	-10.34%
Cash From Operating Activities	-$42.40M	-$140.0M	-$17.32M
YoY Change	144.8%	87.41%	37.79%
INVESTING ACTIVITIES
Capital Expenditures	-$155.0K	$648.0K	-$180.0K
YoY Change	-13.89%	37.0%
Acquisitions
YoY Change
Other Investing Activities	$0.00	$0.00	$0.00
YoY Change		-100.0%	-100.0%
Cash From Investing Activities	-$155.0K	-$648.0K	-$190.0K
YoY Change	-18.42%	-101.75%	-101.15%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	28.80M	$63.65M	1.660M
YoY Change	1634.64%	-72.38%	621.74%
NET CHANGE
Cash From Operating Activities	-42.40M	-$140.0M	-17.32M
Cash From Investing Activities	-155.0K	-$648.0K	-190.0K
Cash From Financing Activities	28.80M	$63.65M	1.660M
Net Change In Cash	-13.76M	-$76.99M	-15.85M
YoY Change	-13.19%	-139.94%	-481.01%
FREE CASH FLOW
Cash From Operating Activities	-$42.40M	-$140.0M	-$17.32M
Capital Expenditures	-$155.0K	$648.0K	-$180.0K
Free Cash Flow	-$42.25M	-$140.6M	-$17.14M
YoY Change	146.47%	87.09%	36.36%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2021	dei	Entity Central Index Key EntityCentralIndexKey	0001442836
CY2021	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2021
CY2021	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2021	dei	Amendment Flag AmendmentFlag	false
CY2021Q4	us-gaap	Finance Lease Liability Current Statement Of Financial Position Extensible List FinanceLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2021-01-31#OtherLiabilitiesCurrent
CY2020Q4	us-gaap	Finance Lease Liability Current Statement Of Financial Position Extensible List FinanceLeaseLiabilityCurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2021-01-31#OtherLiabilitiesCurrent
CY2021Q4	us-gaap	Finance Lease Liability Noncurrent Statement Of Financial Position Extensible List FinanceLeaseLiabilityNoncurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2021-01-31#OtherLiabilitiesNoncurrent
CY2020Q4	us-gaap	Finance Lease Liability Noncurrent Statement Of Financial Position Extensible List FinanceLeaseLiabilityNoncurrentStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2021-01-31#OtherLiabilitiesNoncurrent
CY2021	dei	Document Type DocumentType	10-K
CY2021	dei	Document Period End Date DocumentPeriodEndDate	2021-12-31
CY2021	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2021	dei	Document Annual Report DocumentAnnualReport	true
CY2021Q4	us-gaap	Assets Current AssetsCurrent	188898000	USD
CY2020Q4	us-gaap	Assets Current AssetsCurrent	258580000	USD
CY2021	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2021	dei	Document Transition Report DocumentTransitionReport	false
CY2021	dei	Entity File Number EntityFileNumber	001-38129
CY2021	dei	Entity Registrant Name EntityRegistrantName	Mersana Therapeutics, Inc.
CY2021	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	DE
CY2021	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	04-3562403
CY2021	dei	Entity Address Address Line1 EntityAddressAddressLine1	840 Memorial Drive
CY2021	dei	Entity Address City Or Town EntityAddressCityOrTown	Cambridge
CY2021	dei	Entity Address State Or Province EntityAddressStateOrProvince	MA
CY2021	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	02139
CY2021	dei	City Area Code CityAreaCode	617
CY2021	dei	Local Phone Number LocalPhoneNumber	498-0020
CY2021	dei	Security12b Title Security12bTitle	Common Stock, $0.0001 par value
CY2021	dei	Trading Symbol TradingSymbol	MRSN
CY2021	dei	Security Exchange Name SecurityExchangeName	NASDAQ
CY2021	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	No
CY2021	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2021	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2021	dei	Auditor Location AuditorLocation	Boston, Massachusetts
CY2021	dei	Auditor Firm AuditorFirmId	42
CY2021	dei	Auditor Name AuditorName	Ernst & Young LLP
CY2021	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2021	dei	Entity Small Business EntitySmallBusiness	false
CY2021	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2021	dei	Icfr Auditor Attestation Flag IcfrAuditorAttestationFlag	true
CY2021	dei	Entity Shell Company EntityShellCompany	false
CY2021Q2	dei	Entity Public Float EntityPublicFloat	799836646	USD
CY2022Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	83389806	shares
CY2021Q4	us-gaap	Debt Instrument Carrying Amount DebtInstrumentCarryingAmount	25000000.0	USD
CY2021Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	177947000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	255094000	USD
CY2021Q4	us-gaap	Prepaid Expense And Other Assets Current PrepaidExpenseAndOtherAssetsCurrent	10951000	USD
CY2020Q4	us-gaap	Prepaid Expense And Other Assets Current PrepaidExpenseAndOtherAssetsCurrent	3486000	USD
CY2021Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	1968000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	1730000	USD
CY2021Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	12889000	USD
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	10936000	USD
CY2021Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	2356000	USD
CY2020Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	2153000	USD
CY2021Q4	us-gaap	Assets Assets	206111000	USD
CY2020Q4	us-gaap	Assets Assets	273399000	USD
CY2021Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	12321000	USD
CY2020Q4	us-gaap	Accounts Payable Current AccountsPayableCurrent	8340000	USD
CY2021Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	28716000	USD
CY2020Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	16146000	USD
CY2021Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	3944000	USD
CY2020Q4	us-gaap	Contract With Customer Liability Current ContractWithCustomerLiabilityCurrent	3987000	USD
CY2021Q4	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	2303000	USD
CY2020Q4	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	1437000	USD
CY2021Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	25000000	shares
CY2021Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	239000	USD
CY2020Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	93000	USD
CY2021Q4	us-gaap	Liabilities Current LiabilitiesCurrent	47523000	USD
CY2020Q4	us-gaap	Liabilities Current LiabilitiesCurrent	30003000	USD
CY2021Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	11247000	USD
CY2020Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	10158000	USD
CY2021Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	24626000	USD
CY2020Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	4977000	USD
CY2021Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	974000	USD
CY2020Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	174000	USD
CY2021Q4	us-gaap	Liabilities Liabilities	84370000	USD
CY2020Q4	us-gaap	Liabilities Liabilities	45312000	USD
CY2021Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2020Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2021Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.0001
CY2020Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.0001
CY2020Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	25000000	shares
CY2020Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2021Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2020Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2021Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2021Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	USD
CY2020Q4	us-gaap	Preferred Stock Value PreferredStockValue	0	USD
CY2020Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.0001
CY2021Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.0001
CY2020Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	175000000	shares
CY2021Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	175000000	shares
CY2021Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	73709056	shares
CY2021Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	73709056	shares
CY2020Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	68841288	shares
CY2020Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	68841288	shares
CY2021Q4	us-gaap	Stockholders Equity StockholdersEquity	121741000	USD
CY2021Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	206111000	USD
CY2020Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	273399000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	228087000	USD
CY2021Q4	us-gaap	Common Stock Value CommonStockValue	7000	USD
CY2020Q4	us-gaap	Common Stock Value CommonStockValue	7000	USD
CY2021Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	572213000	USD
CY2020Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	508499000	USD
CY2021Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-450479000	USD
CY2020Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-280419000	USD
CY2021	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	43000	USD
CY2020	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	828000	USD
CY2019	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	42123000	USD
CY2021	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	132013000	USD
CY2020	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	67036000	USD
CY2019	us-gaap	Research And Development Expense ResearchAndDevelopmentExpense	55040000	USD
CY2021	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	36888000	USD
CY2020	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	21902000	USD
CY2019	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	17283000	USD
CY2021	us-gaap	Operating Expenses OperatingExpenses	168901000	USD
CY2020	us-gaap	Operating Expenses OperatingExpenses	88938000	USD
CY2019	us-gaap	Operating Expenses OperatingExpenses	72323000	USD
CY2021	us-gaap	Investment Income Interest InvestmentIncomeInterest	65000	USD
CY2020	us-gaap	Investment Income Interest InvestmentIncomeInterest	424000	USD
CY2019	us-gaap	Investment Income Interest InvestmentIncomeInterest	2226000	USD
CY2021	us-gaap	Interest Expense InterestExpense	1267000	USD
CY2020	us-gaap	Interest Expense InterestExpense	359000	USD
CY2019	us-gaap	Interest Expense InterestExpense	234000	USD
CY2021	us-gaap	Nonoperating Income Expense NonoperatingIncomeExpense	-1202000	USD
CY2020	us-gaap	Nonoperating Income Expense NonoperatingIncomeExpense	65000	USD
CY2019	us-gaap	Nonoperating Income Expense NonoperatingIncomeExpense	1992000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	-170060000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	-88045000	USD
CY2020	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-88070000	USD
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	-88045000	USD
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	-88045000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-28175000	USD
CY2021	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	-170060000	USD
CY2021	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	-170060000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	-28208000	USD
CY2021	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	0	USD
CY2020	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	-25000	USD
CY2019	us-gaap	Other Comprehensive Income Availableforsale Securities Adjustment Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent	33000	USD
CY2021	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	-170060000	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Diluted NetIncomeLossAvailableToCommonStockholdersDiluted	-28208000	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	-28208000	USD
CY2021	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	-2.41
CY2021	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	-2.41
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	-1.43
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	-1.43
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	-0.65
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	-0.65
CY2021	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	70580949	shares
CY2021	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	70580949	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	61485205	shares
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	61485205	shares
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	43492113	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	43492113	shares
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	8795000	USD
CY2019	mrsn	Stock Issuance Discounts And Commissions On Transaction StockIssuanceDiscountsAndCommissionsOnTransaction	5587000	USD
CY2019	mrsn	Stock Issued During Period Value Stock Options And Warrants Exercised StockIssuedDuringPeriodValueStockOptionsAndWarrantsExercised	175000	USD
CY2019	us-gaap	Adjustments To Additional Paid In Capital Share Based Compensation Employee Stock Purchase Program Requisite Service Period Recognition AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationEmployeeStockPurchaseProgramRequisiteServicePeriodRecognition	489000	USD
CY2019	mrsn	Stock Retired During Period Exchanged For Common Stock Warrant Value StockRetiredDuringPeriodExchangedForCommonStockWarrantValue	8986000	USD
CY2019	us-gaap	Adjustments To Additional Paid In Capital Warrant Issued AdjustmentsToAdditionalPaidInCapitalWarrantIssued	8986000	USD
CY2019	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	4872000	USD
CY2020	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	7172000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-25000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	-88045000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	33000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	-28208000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	78318000	USD
CY2020	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	3138000	USD
CY2020	us-gaap	Adjustments To Additional Paid In Capital Share Based Compensation Employee Stock Purchase Program Requisite Service Period Recognition AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationEmployeeStockPurchaseProgramRequisiteServicePeriodRecognition	561000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	228087000	USD
CY2021	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	1837000	USD
CY2021	us-gaap	Adjustments Related To Tax Withholding For Share Based Compensation AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation	259000	USD
CY2021	us-gaap	Adjustments To Additional Paid In Capital Share Based Compensation Employee Stock Purchase Program Requisite Service Period Recognition AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationEmployeeStockPurchaseProgramRequisiteServicePeriodRecognition	640000	USD
CY2021	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	18409000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	-170060000	USD
CY2021Q4	us-gaap	Stockholders Equity StockholdersEquity	121741000	USD
CY2021	us-gaap	Profit Loss ProfitLoss	-170060000	USD
CY2021	mrsn	Proceeds From Debt Net Issuance Costs ProceedsFromDebtNetIssuanceCosts	24042000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	-88045000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	-28208000	USD
CY2021	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	855000	USD
CY2020	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	1010000	USD
CY2019	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	1245000	USD
CY2021	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	0	USD
CY2020	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	86000	USD
CY2019	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	222000	USD
CY2021	us-gaap	Share Based Compensation ShareBasedCompensation	18409000	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	7172000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	4872000	USD
CY2021	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-723000	USD
CY2020	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-148000	USD
CY2019	us-gaap	Other Noncash Income Expense OtherNoncashIncomeExpense	-103000	USD
CY2021	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	0	USD
CY2020	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	0	USD
CY2019	us-gaap	Increase Decrease In Accounts Receivable IncreaseDecreaseInAccountsReceivable	-459000	USD
CY2021	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	12570000	USD
CY2020	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	7280000	USD
CY2019	us-gaap	Increase Decrease In Accrued Liabilities IncreaseDecreaseInAccruedLiabilities	-3569000	USD
CY2021	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	2734000	USD
CY2020	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	1950000	USD
CY2019	us-gaap	Increase Decrease In Prepaid Deferred Expense And Other Assets IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets	-2179000	USD
CY2021	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	718000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	700000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	0	USD
CY2021	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	483000	USD
CY2020	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	942000	USD
CY2019	us-gaap	Increase Decrease In Accounts Payable IncreaseDecreaseInAccountsPayable	-3110000	USD
CY2021	mrsn	Increase Decrease In Operating Lease Assets IncreaseDecreaseInOperatingLeaseAssets	-1829000	USD
CY2020	mrsn	Increase Decrease In Operating Lease Assets IncreaseDecreaseInOperatingLeaseAssets	-1642000	USD
CY2019	mrsn	Increase Decrease In Operating Lease Assets IncreaseDecreaseInOperatingLeaseAssets	-1771000	USD
CY2021	us-gaap	Increase Decrease In Operating Lease Liability IncreaseDecreaseInOperatingLeaseLiability	-1827000	USD
CY2020	us-gaap	Increase Decrease In Operating Lease Liability IncreaseDecreaseInOperatingLeaseLiability	-1281000	USD
CY2019	us-gaap	Increase Decrease In Operating Lease Liability IncreaseDecreaseInOperatingLeaseLiability	-1883000	USD
CY2021	us-gaap	Increase Decrease In Contract With Customer Liability IncreaseDecreaseInContractWithCustomerLiability	-43000	USD
CY2020	us-gaap	Increase Decrease In Contract With Customer Liability IncreaseDecreaseInContractWithCustomerLiability	-828000	USD
CY2019	us-gaap	Increase Decrease In Contract With Customer Liability IncreaseDecreaseInContractWithCustomerLiability	-41381000	USD
CY2021	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	525000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	0	USD
CY2019	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	0	USD
CY2021	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-139988000	USD
CY2020	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-74696000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	-67744000	USD
CY2021	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	0	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	37500000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	27000000	USD
CY2021	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	0	USD
CY2020	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	0	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	37027000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-27293000	USD
CY2021	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	1837000	USD
CY2020	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	3138000	USD
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	53688000	USD
CY2021	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	648000	USD
CY2020	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	473000	USD
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	605000	USD
CY2021	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-648000	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	175000	USD
CY2021	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlans	640000	USD
CY2020	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlans	561000	USD
CY2019	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlans	489000	USD
CY2021	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	259000	USD
CY2020	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	0	USD
CY2019	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	0	USD
CY2021	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	609000	USD
CY2020	mrsn	Proceeds From Debt Net Issuance Costs ProceedsFromDebtNetIssuanceCosts	-197000	USD
CY2019	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	87000	USD
CY2021	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	63646000	USD
CY2020	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	116000	USD
CY2021Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	178425000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	255415000	USD
CY2019	mrsn	Proceeds From Debt Net Issuance Costs ProceedsFromDebtNetIssuanceCosts	4965000	USD
CY2021	us-gaap	Repayments Of Debt RepaymentsOfDebt	5486000	USD
CY2020	us-gaap	Repayments Of Debt RepaymentsOfDebt	0	USD
CY2019	us-gaap	Repayments Of Debt RepaymentsOfDebt	0	USD
CY2021	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	215000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	230412000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	97704000	USD
CY2021	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-76990000	USD
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	192743000	USD
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	2667000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	255415000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	62672000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	60005000	USD
CY2021	us-gaap	Debt Issuance Costs Incurred During Noncash Or Partial Noncash Transaction DebtIssuanceCostsIncurredDuringNoncashOrPartialNoncashTransaction	0	USD
CY2020	us-gaap	Debt Issuance Costs Incurred During Noncash Or Partial Noncash Transaction DebtIssuanceCostsIncurredDuringNoncashOrPartialNoncashTransaction	0	USD
CY2019	us-gaap	Debt Issuance Costs Incurred During Noncash Or Partial Noncash Transaction DebtIssuanceCostsIncurredDuringNoncashOrPartialNoncashTransaction	180000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	62672000	USD
CY2021	mrsn	Fair Value Of Common Stock Retired In Exchange For Issuance Of Common Stock Warrant FairValueOfCommonStockRetiredInExchangeForIssuanceOfCommonStockWarrant	0	USD
CY2020	mrsn	Fair Value Of Common Stock Retired In Exchange For Issuance Of Common Stock Warrant FairValueOfCommonStockRetiredInExchangeForIssuanceOfCommonStockWarrant	0	USD
CY2019	mrsn	Fair Value Of Common Stock Retired In Exchange For Issuance Of Common Stock Warrant FairValueOfCommonStockRetiredInExchangeForIssuanceOfCommonStockWarrant	8986000	USD
CY2021	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	0	USD
CY2020	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	102000	USD
CY2019	us-gaap	Capital Expenditures Incurred But Not Yet Paid CapitalExpendituresIncurredButNotYetPaid	0	USD
CY2021	us-gaap	Interest Paid Net InterestPaidNet	429000	USD
CY2020	us-gaap	Interest Paid Net InterestPaidNet	234000	USD
CY2019	us-gaap	Interest Paid Net InterestPaidNet	132000	USD
CY2021	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	3783000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	9980000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	4369000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	0	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	429000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	-170060000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	-88045000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	-28208000	USD
CY2021Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	-450479000	USD
CY2021	us-gaap	Use Of Estimates UseOfEstimates	<div style="margin-top:12pt;text-align:justify"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Use of Estimates</span></div><div style="margin-top:12pt;text-align:justify"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The preparation of the Company's consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenue, expenses and related disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenue and expenses during the reporting period. On an ongoing basis, the Company's management evaluates its estimates which include, but are not limited to, management's judgments with respect to the identification of performance obligations and standalone selling prices of those performance obligations within its revenue arrangements, accrued preclinical, manufacturing and clinical expenses, valuation of stock-based awards and income taxes. Actual results could differ from those estimates.</span></div>
CY2021	mrsn	Revenue Collection Period RevenueCollectionPeriod	P30D
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	255094000	USD
CY2021Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	177947000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	62351000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	255094000	USD
CY2020Q4	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	321000	USD
CY2021Q4	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	478000	USD
CY2019Q4	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	321000	USD
CY2020Q4	us-gaap	Restricted Cash Noncurrent RestrictedCashNoncurrent	321000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	255415000	USD
CY2021Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	178425000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	62672000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	255415000	USD
CY2021Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	2356000	USD
CY2020Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	2153000	USD
CY2021Q4	us-gaap	Retainage Deposit RetainageDeposit	1418000	USD
CY2020Q4	us-gaap	Retainage Deposit RetainageDeposit	1832000	USD
CY2021Q4	us-gaap	Security Deposit SecurityDeposit	478000	USD
CY2020Q4	us-gaap	Security Deposit SecurityDeposit	321000	USD
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2021	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	9199512	shares
CY2020	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	6869189	shares
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	5207582	shares
CY2020	us-gaap	Asset Impairment Charges AssetImpairmentCharges	0	USD
CY2019	us-gaap	Asset Impairment Charges AssetImpairmentCharges	0	USD
CY2021	us-gaap	Asset Impairment Charges AssetImpairmentCharges	0	USD
CY2021Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	3944000	USD
CY2019Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	0	USD
CY2021	us-gaap	Concentration Risk Credit Risk ConcentrationRiskCreditRisk	<div style="margin-top:12pt;text-align:justify"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-style:italic;font-weight:700;line-height:120%">Concentration of Credit Risk and Off-balance Sheet Risk</span></div><div style="margin-top:12pt;text-align:justify"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The Company has no financial instruments with off-balance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially subject the Company to concentrations of credit risk </span></div>primarily consist of cash equivalents and marketable securities. Under its investment policy, the Company limits amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. The Company has not experienced any credit losses and does not believe that it is subject to any significant concentrations of credit risk from these financial instruments.
CY2021	us-gaap	Concentration Risk Credit Risk Financial Instrument Maximum Exposure ConcentrationRiskCreditRiskFinancialInstrumentMaximumExposure	0	USD
CY2020Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	0	USD
CY2021Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	0	USD
CY2020Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	3987000	USD
CY2021	mrsn	Contract With Customer Liability Increase ContractWithCustomerLiabilityIncrease	0	USD
CY2021	mrsn	Contract With Customer Liability Decrease ContractWithCustomerLiabilityDecrease	43000	USD
CY2020Q4	us-gaap	Contract With Customer Asset Net ContractWithCustomerAssetNet	0	USD
CY2019Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	4815000	USD
CY2020	mrsn	Contract With Customer Liability Increase ContractWithCustomerLiabilityIncrease	0	USD
CY2020	mrsn	Contract With Customer Liability Decrease ContractWithCustomerLiabilityDecrease	828000	USD
CY2020Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	3987000	USD
CY2021	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	43000	USD
CY2020	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	828000	USD
CY2021	us-gaap	Contract With Customer Performance Obligation Satisfied In Previous Period ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod	0	USD
CY2020	us-gaap	Contract With Customer Performance Obligation Satisfied In Previous Period ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod	0	USD
CY2020	us-gaap	Depreciation Depreciation	1010000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	2.47
CY2021Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Before Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization	9650000	USD
CY2020Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Before Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization	9365000	USD
CY2021Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization	7682000	USD
CY2020Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization	7635000	USD
CY2021Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset After Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	1968000	USD
CY2020Q4	us-gaap	Property Plant And Equipment And Finance Lease Right Of Use Asset After Accumulated Depreciation And Amortization PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	1730000	USD
CY2021	us-gaap	Depreciation Depreciation	855000	USD
CY2019	us-gaap	Depreciation Depreciation	1245000	USD
CY2021Q4	mrsn	Accrued Manufacturing Expenses Current AccruedManufacturingExpensesCurrent	8476000	USD
CY2020Q4	mrsn	Accrued Manufacturing Expenses Current AccruedManufacturingExpensesCurrent	4157000	USD
CY2021Q4	mrsn	Accrued Clinical Expenses Current AccruedClinicalExpensesCurrent	7879000	USD
CY2020Q4	mrsn	Accrued Clinical Expenses Current AccruedClinicalExpensesCurrent	5126000	USD
CY2021Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	7319000	USD
CY2020Q4	us-gaap	Employee Related Liabilities Current EmployeeRelatedLiabilitiesCurrent	5412000	USD
CY2021Q4	mrsn	Accrued Preclinical Expenses Current AccruedPreclinicalExpensesCurrent	3848000	USD
CY2020Q4	mrsn	Accrued Preclinical Expenses Current AccruedPreclinicalExpensesCurrent	619000	USD
CY2021Q4	us-gaap	Accrued Professional Fees Current AccruedProfessionalFeesCurrent	909000	USD
CY2020Q4	us-gaap	Accrued Professional Fees Current AccruedProfessionalFeesCurrent	757000	USD
CY2021Q4	us-gaap	Other Accrued Liabilities Current OtherAccruedLiabilitiesCurrent	285000	USD
CY2020Q4	us-gaap	Other Accrued Liabilities Current OtherAccruedLiabilitiesCurrent	75000	USD
CY2021Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	28716000	USD
CY2020Q4	us-gaap	Accrued Liabilities Current AccruedLiabilitiesCurrent	16146000	USD
CY2021Q4	us-gaap	Debt Instrument Carrying Amount DebtInstrumentCarryingAmount	25000000	USD
CY2021Q4	us-gaap	Long Term Debt Current LongTermDebtCurrent	0	USD
CY2021Q4	mrsn	Debt Instrument Carrying Amount Noncurrent DebtInstrumentCarryingAmountNoncurrent	25000000	USD
CY2021Q4	us-gaap	Deferred Finance Costs Net DeferredFinanceCostsNet	410000	USD
CY2021Q4	us-gaap	Debt Instrument Unamortized Premium DebtInstrumentUnamortizedPremium	36000	USD
CY2021Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	24626000	USD
CY2021Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Next Twelve Months LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths	0	USD
CY2021Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Two LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo	0	USD
CY2021Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Three LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree	2083000	USD
CY2021Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Four LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour	12500000	USD
CY2021Q4	us-gaap	Long Term Debt Maturities Repayments Of Principal In Year Five LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive	10417000	USD
CY2021Q4	us-gaap	Debt Instrument Carrying Amount DebtInstrumentCarryingAmount	25000000	USD
CY2021	us-gaap	Interest Expense Debt InterestExpenseDebt	797000	USD
CY2020	us-gaap	Interest Expense Debt InterestExpenseDebt	340000	USD
CY2021Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	25000000	shares
CY2021Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2013	mrsn	Class Of Warrant Or Right Securities Called By Warrants Or Rights Number Issued ClassOfWarrantOrRightSecuritiesCalledByWarrantsOrRightsNumberIssued	129491	shares
CY2013Q4	us-gaap	Class Of Warrant Or Right Exercise Price Of Warrants Or Rights1 ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1	0.05
CY2013	mrsn	Contractual Life Of Warrants ContractualLifeOfWarrants	P10Y
CY2020Q4	us-gaap	Class Of Warrant Or Right Outstanding ClassOfWarrantOrRightOutstanding	39474	shares
CY2021Q4	us-gaap	Class Of Warrant Or Right Outstanding ClassOfWarrantOrRightOutstanding	39474	shares
CY2021	mrsn	Stock Issued During Period Shares Warrants Exercised StockIssuedDuringPeriodSharesWarrantsExercised	0	shares
CY2021Q4	us-gaap	Common Stock Capital Shares Reserved For Future Issuance CommonStockCapitalSharesReservedForFutureIssuance	9199512	shares
CY2020Q4	us-gaap	Common Stock Capital Shares Reserved For Future Issuance CommonStockCapitalSharesReservedForFutureIssuance	6869189	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	6112948	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	7.84
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P7Y3M18D
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	114729000	USD
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	3308220	shares
CY2021	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	16.78
CY2021	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	421381	shares
CY2021	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	4.36
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Expirations In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod	657358	shares
CY2021	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Expirations In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice	11.76
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	8342429	shares
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	11.25
CY2021	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P7Y2M12D
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	8458000	USD
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber	8342429	shares
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice	11.25
CY2021	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	P7Y2M12D
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue	8458000	USD
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber	3997529	shares
CY2021Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	7.63
CY2021	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P5Y6M
CY2021Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	7539000	USD
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	11.71
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	7.99
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	4299000	USD
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	11147000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Total Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue	202000	USD
CY2021	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	1837000	USD
CY2020	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	3138000	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	175000	USD
CY2021	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	18409000	USD
CY2020	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	7172000	USD
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	4872000	USD
CY2021	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	18409000	USD
CY2020	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	7172000	USD
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	4872000	USD
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.009
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.012
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.023
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2021	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y21D
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y18D
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y11M26D
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.82
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.74
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.74
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2021Q2	mrsn	Increase Decrease In Operating Lease Liabilities IncreaseDecreaseInOperatingLeaseLiabilities	3783000	USD
CY2021Q2	mrsn	Increase Decrease In Operating Lease Right Of Use Asset IncreaseDecreaseInOperatingLeaseRightOfUseAsset	3783000	USD
CY2021Q4	us-gaap	Security Deposit SecurityDeposit	478000	USD
CY2020Q4	us-gaap	Security Deposit SecurityDeposit	321000	USD
CY2021	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	609000	USD
CY2021	us-gaap	Operating Lease Cost OperatingLeaseCost	3502000	USD
CY2020	us-gaap	Operating Lease Cost OperatingLeaseCost	2755000	USD
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	2160000	USD
CY2021	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	169000	USD
CY2020	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	101000	USD
CY2019	us-gaap	Finance Lease Right Of Use Asset Amortization FinanceLeaseRightOfUseAssetAmortization	75000	USD
CY2021	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	28000	USD
CY2020	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	21000	USD
CY2019	us-gaap	Finance Lease Interest Expense FinanceLeaseInterestExpense	20000	USD
CY2021	mrsn	Finance Lease Cost FinanceLeaseCost	197000	USD
CY2020	mrsn	Finance Lease Cost FinanceLeaseCost	122000	USD
CY2019	mrsn	Finance Lease Cost FinanceLeaseCost	95000	USD
CY2021Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	12889000	USD
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	10936000	USD
CY2021Q4	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	2303000	USD
CY2020Q4	us-gaap	Operating Lease Liability Current OperatingLeaseLiabilityCurrent	1437000	USD
CY2021Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	11247000	USD
CY2020Q4	us-gaap	Operating Lease Liability Noncurrent OperatingLeaseLiabilityNoncurrent	10158000	USD
CY2021Q4	us-gaap	Finance Lease Right Of Use Asset Before Accumulated Amortization FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization	1038000	USD
CY2020Q4	us-gaap	Finance Lease Right Of Use Asset Before Accumulated Amortization FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization	429000	USD
CY2021Q4	us-gaap	Finance Lease Right Of Use Asset Accumulated Amortization FinanceLeaseRightOfUseAssetAccumulatedAmortization	345000	USD
CY2020Q4	us-gaap	Finance Lease Right Of Use Asset Accumulated Amortization FinanceLeaseRightOfUseAssetAccumulatedAmortization	176000	USD
CY2021Q4	us-gaap	Finance Lease Liability Current FinanceLeaseLiabilityCurrent	239000	USD
CY2020Q4	us-gaap	Finance Lease Liability Current FinanceLeaseLiabilityCurrent	93000	USD
CY2021Q4	us-gaap	Finance Lease Liability Noncurrent FinanceLeaseLiabilityNoncurrent	449000	USD
CY2020Q4	us-gaap	Finance Lease Liability Noncurrent FinanceLeaseLiabilityNoncurrent	174000	USD
CY2021Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P4Y3M18D
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P5Y2M12D
CY2021Q4	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P4Y
CY2020Q4	us-gaap	Finance Lease Weighted Average Remaining Lease Term1 FinanceLeaseWeightedAverageRemainingLeaseTerm1	P2Y10M24D
CY2021Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.108
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.108
CY2021Q4	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.054
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	2394000	USD
CY2021	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	28000	USD
CY2020	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	21000	USD
CY2020Q4	us-gaap	Finance Lease Weighted Average Discount Rate Percent FinanceLeaseWeightedAverageDiscountRatePercent	0.069
CY2021	us-gaap	Operating Lease Payments OperatingLeasePayments	3241000	USD
CY2021	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	215000	USD
CY2020	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	116000	USD
CY2021	us-gaap	Lease Cost LeaseCost	3390000	USD
CY2020	us-gaap	Lease Cost LeaseCost	2644000	USD
CY2019	us-gaap	Lease Cost LeaseCost	2160000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	1310000	USD
CY2021Q4	us-gaap	Finance Lease Liability Payments Due Year Five FinanceLeaseLiabilityPaymentsDueYearFive	8000	USD
CY2021	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense EffectiveIncomeTaxRateReconciliationNondeductibleExpense	-0.002
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense EffectiveIncomeTaxRateReconciliationNondeductibleExpense	0.012
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	3795000	USD
CY2021Q4	us-gaap	Finance Lease Liability Payments Due Next Twelve Months FinanceLeaseLiabilityPaymentsDueNextTwelveMonths	269000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	3909000	USD
CY2021Q4	us-gaap	Finance Lease Liability Payments Due Year Two FinanceLeaseLiabilityPaymentsDueYearTwo	262000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	4027000	USD
CY2021Q4	us-gaap	Finance Lease Liability Payments Due Year Three FinanceLeaseLiabilityPaymentsDueYearThree	141000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	4147000	USD
CY2021Q4	us-gaap	Finance Lease Liability Payments Due Year Four FinanceLeaseLiabilityPaymentsDueYearFour	48000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	17188000	USD
CY2021Q4	us-gaap	Finance Lease Liability Payments Due FinanceLeaseLiabilityPaymentsDue	728000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	3638000	USD
CY2021Q4	us-gaap	Finance Lease Liability Undiscounted Excess Amount FinanceLeaseLiabilityUndiscountedExcessAmount	40000	USD
CY2021Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	13550000	USD
CY2021Q4	us-gaap	Finance Lease Liability FinanceLeaseLiability	688000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	0	USD
CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	0	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	0	USD
CY2021	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2020	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2021	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.063
CY2020	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.067
CY2019	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.061
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.034
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.103
CY2021	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.001
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense EffectiveIncomeTaxRateReconciliationNondeductibleExpense	-0.020
CY2021	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.038
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0
CY2021	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.533
CY2021	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	-0.310
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	-0.323
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	0.179
CY2021	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0
CY2020	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0
CY2021Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	106055000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	64259000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	12424000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards DeferredTaxAssetsTaxCreditCarryforwards	5670000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Accrued Liabilities DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities	6892000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Accrued Liabilities DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities	4058000	USD
CY2021Q4	mrsn	Deferred Tax Assets Lease Liabilities DeferredTaxAssetsLeaseLiabilities	3698000	USD
CY2020Q4	mrsn	Deferred Tax Assets Lease Liabilities DeferredTaxAssetsLeaseLiabilities	3166000	USD
CY2021Q4	mrsn	Deferred Tax Assets Licensed Technology DeferredTaxAssetsLicensedTechnology	2775000	USD
CY2020Q4	mrsn	Deferred Tax Assets Licensed Technology DeferredTaxAssetsLicensedTechnology	1534000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Deferred Income DeferredTaxAssetsDeferredIncome	1076000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Deferred Income DeferredTaxAssetsDeferredIncome	1088000	USD
CY2021Q4	mrsn	Deferred Tax Assets Depreciation DeferredTaxAssetsDepreciation	493000	USD
CY2020Q4	mrsn	Deferred Tax Assets Depreciation DeferredTaxAssetsDepreciation	502000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	71000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	84000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	133484000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	80361000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	130051000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	77375000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	3433000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	2986000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Leasing Arrangements DeferredTaxLiabilitiesLeasingArrangements	3433000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Leasing Arrangements DeferredTaxLiabilitiesLeasingArrangements	2986000	USD
CY2021Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	3433000	USD
CY2020Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	2986000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	0	USD
CY2021Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	130051000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	77375000	USD
CY2021	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	52676000	USD
CY2020	us-gaap	Valuation Allowance Deferred Tax Asset Change In Amount ValuationAllowanceDeferredTaxAssetChangeInAmount	28468000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0	USD
CY2021Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	0	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	0	USD
CY2021Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	0	USD
CY2021Q4	mrsn	Income Taxes Number Of State Jurisdictions IncomeTaxesNumberOfStateJurisdictions	4	jurisdiction
CY2021Q4	mrsn	Income Taxes Number Of Audits In Progress IncomeTaxesNumberOfAuditsInProgress	0	audit
CY2021	mrsn	Defined Contribution Plan Eligible Age To Participate DefinedContributionPlanEligibleAgeToParticipate	P21Y
CY2021	us-gaap	Defined Contribution Plan Maximum Annual Contributions Per Employee Percent DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent	0.95
	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent Of Match DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	0.50
	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent DefinedContributionPlanEmployerMatchingContributionPercent	0.06
	mrsn	Defined Contribution Plan Maximum Annual Employer Contribution Per Employee Amount DefinedContributionPlanMaximumAnnualEmployerContributionPerEmployeeAmount	6000	USD
CY2021	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent Of Match DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	1
	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent Of Match DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	1
CY2021	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent DefinedContributionPlanEmployerMatchingContributionPercent	0.04
	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent DefinedContributionPlanEmployerMatchingContributionPercent	0.04
CY2021	mrsn	Defined Contribution Plan Maximum Annual Employer Contribution Per Employee Amount DefinedContributionPlanMaximumAnnualEmployerContributionPerEmployeeAmount	7000	USD
	mrsn	Defined Contribution Plan Maximum Annual Employer Contribution Per Employee Amount DefinedContributionPlanMaximumAnnualEmployerContributionPerEmployeeAmount	7000	USD
CY2021	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	764000	USD
CY2020	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	486000	USD
CY2019	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	404000	USD

Files In Submission

Name	View Source	Status
0001628280-22-004101-index-headers.html	Edgar Link	pending
0001628280-22-004101-index.html	Edgar Link	pending
0001628280-22-004101.txt	Edgar Link	pending
0001628280-22-004101-xbrl.zip	Edgar Link	pending
exhibit101410kfy2021.htm	Edgar Link	pending
exhibit101510kfy2021.htm	Edgar Link	pending
exhibit102810kfy2021.htm	Edgar Link	pending
exhibit102910kfy2021.htm	Edgar Link	pending
exhibit103010kfy2021.htm	Edgar Link	pending
exhibit21110kfy2021q4.htm	Edgar Link	pending
exhibit23110kfy2021q4.htm	Edgar Link	pending
exhibit31110kfy2021q4.htm	Edgar Link	pending
exhibit31210kfy2021q4.htm	Edgar Link	pending
exhibit32110kfy2021q4.htm	Edgar Link	pending
FilingSummary.xml	Edgar Link	unprocessable
Financial_Report.xlsx	Edgar Link	pending
MetaLinks.json	Edgar Link	pending
mrsn-20211231.htm	Edgar Link	pending
mrsn-20211231.xsd	Edgar Link	pending
mrsn-20211231_cal.xml	Edgar Link	unprocessable
mrsn-20211231_def.xml	Edgar Link	unprocessable
mrsn-20211231_g1.jpg	Edgar Link	pending
mrsn-20211231_g2.jpg	Edgar Link	pending
mrsn-20211231_htm.xml	Edgar Link	completed
mrsn-20211231_lab.xml	Edgar Link	unprocessable
mrsn-20211231_pre.xml	Edgar Link	unprocessable
R1.htm	Edgar Link	pending
R10.htm	Edgar Link	pending
R11.htm	Edgar Link	pending
R12.htm	Edgar Link	pending
R13.htm	Edgar Link	pending
R14.htm	Edgar Link	pending
R15.htm	Edgar Link	pending
R16.htm	Edgar Link	pending
R17.htm	Edgar Link	pending
R18.htm	Edgar Link	pending
R19.htm	Edgar Link	pending
R2.htm	Edgar Link	pending
R20.htm	Edgar Link	pending
R21.htm	Edgar Link	pending
R22.htm	Edgar Link	pending
R23.htm	Edgar Link	pending
R24.htm	Edgar Link	pending
R25.htm	Edgar Link	pending
R26.htm	Edgar Link	pending
R27.htm	Edgar Link	pending
R28.htm	Edgar Link	pending
R29.htm	Edgar Link	pending
R3.htm	Edgar Link	pending
R30.htm	Edgar Link	pending
R31.htm	Edgar Link	pending
R32.htm	Edgar Link	pending
R33.htm	Edgar Link	pending
R34.htm	Edgar Link	pending
R35.htm	Edgar Link	pending
R36.htm	Edgar Link	pending
R37.htm	Edgar Link	pending
R38.htm	Edgar Link	pending
R39.htm	Edgar Link	pending
R4.htm	Edgar Link	pending
R40.htm	Edgar Link	pending
R41.htm	Edgar Link	pending
R42.htm	Edgar Link	pending
R43.htm	Edgar Link	pending
R44.htm	Edgar Link	pending
R45.htm	Edgar Link	pending
R46.htm	Edgar Link	pending
R47.htm	Edgar Link	pending
R48.htm	Edgar Link	pending
R49.htm	Edgar Link	pending
R5.htm	Edgar Link	pending
R50.htm	Edgar Link	pending
R51.htm	Edgar Link	pending
R52.htm	Edgar Link	pending
R53.htm	Edgar Link	pending
R54.htm	Edgar Link	pending
R55.htm	Edgar Link	pending
R56.htm	Edgar Link	pending
R57.htm	Edgar Link	pending
R58.htm	Edgar Link	pending
R59.htm	Edgar Link	pending
R6.htm	Edgar Link	pending
R60.htm	Edgar Link	pending
R61.htm	Edgar Link	pending
R62.htm	Edgar Link	pending
R63.htm	Edgar Link	pending
R64.htm	Edgar Link	pending
R65.htm	Edgar Link	pending
R66.htm	Edgar Link	pending
R67.htm	Edgar Link	pending
R68.htm	Edgar Link	pending
R7.htm	Edgar Link	pending
R8.htm	Edgar Link	pending
R9.htm	Edgar Link	pending
report.css	Edgar Link	pending
Show.js	Edgar Link	pending

Create your account

Find Stocks Worth Researching

Deeply Understand Businesses

Value Businesses Intelligently

$MRSN
Mersana Therapeutics, Inc. Stock $mrsn

2021 Q4 Form 10-K Financial Statement

#000162828022004101 Filed on February 28, 2022

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$MRSN Mersana Therapeutics, Inc. Stock $mrsn

2021 Q4 Form 10-K Financial Statement

#000162828022004101 Filed on February 28, 2022

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$MRSN
Mersana Therapeutics, Inc. Stock $mrsn