3.21.2 html 185 303 1 false 56 0 false 5 false false R1.htm 100000 - Document - Cover Page Sheet http://sierraoncology.com/20210930/taxonomy/role/DocumentCoverPage Cover Page Cover 1 false false R2.htm 100010 - Statement - Condensed Consolidated Balance Sheets Sheet http://sierraoncology.com/20210930/taxonomy/role/StatementCondensedConsolidatedBalanceSheets Condensed Consolidated Balance Sheets Statements 2 false false R3.htm 100020 - Statement - Condensed Consolidated Balance Sheets (Parenthetical) Sheet http://sierraoncology.com/20210930/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParenthetical Condensed Consolidated Balance Sheets (Parenthetical) Statements 3 false false R4.htm 100030 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss Sheet http://sierraoncology.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLoss Condensed Consolidated Statements of Operations and Comprehensive Loss Statements 4 false false R5.htm 100040 - Statement - Condensed Consolidated Statements of Stockholders' Equity Sheet http://sierraoncology.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfStockholdersEquity Condensed Consolidated Statements of Stockholders' Equity Statements 5 false false R6.htm 100050 - Statement - Condensed Consolidated Statements of Cash Flows Sheet http://sierraoncology.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlows Condensed Consolidated Statements of Cash Flows Statements 6 false false R7.htm 100060 - Disclosure - Organization Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureOrganization Organization Notes 7 false false R8.htm 100070 - Disclosure - Summary of Significant Accounting Policies Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 8 false false R9.htm 100080 - Disclosure - Net Loss Per Share Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureNetLossPerShare Net Loss Per Share Notes 9 false false R10.htm 100090 - Disclosure - Fair Value Measurements Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureFairValueMeasurements Fair Value Measurements Notes 10 false false R11.htm 100100 - Disclosure - Balance Sheet Components Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponents Balance Sheet Components Notes 11 false false R12.htm 100110 - Disclosure - Leases Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureLeases Leases Notes 12 false false R13.htm 100120 - Disclosure - Commitments and Contingencies Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingencies Commitments and Contingencies Notes 13 false false R14.htm 100130 - Disclosure - Stockholders' Equity Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockholdersEquity Stockholders' Equity Notes 14 false false R15.htm 100140 - Disclosure - Stock-Based Compensation Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensation Stock-Based Compensation Notes 15 false false R16.htm 100150 - Disclosure - Income Taxes Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureIncomeTaxes Income Taxes Notes 16 false false R17.htm 100160 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://sierraoncology.com/20210930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies 17 false false R18.htm 100170 - Disclosure - Net Loss Per Share (Tables) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureNetLossPerShareTables Net Loss Per Share (Tables) Tables http://sierraoncology.com/20210930/taxonomy/role/DisclosureNetLossPerShare 18 false false R19.htm 100180 - Disclosure - Fair Value Measurements (Tables) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://sierraoncology.com/20210930/taxonomy/role/DisclosureFairValueMeasurements 19 false false R20.htm 100190 - Disclosure - Balance Sheet Components (Tables) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsTables Balance Sheet Components (Tables) Tables http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponents 20 false false R21.htm 100200 - Disclosure - Leases (Tables) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureLeasesTables Leases (Tables) Tables http://sierraoncology.com/20210930/taxonomy/role/DisclosureLeases 21 false false R22.htm 100210 - Disclosure - Stockholders' Equity (Tables) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockholdersEquityTables Stockholders' Equity (Tables) Tables http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockholdersEquity 22 false false R23.htm 100220 - Disclosure - Stock-Based Compensation (Tables) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensationTables Stock-Based Compensation (Tables) Tables http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensation 23 false false R24.htm 100230 - Disclosure - Organization - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureOrganizationAdditionalInformationDetail Organization - Additional Information (Detail) Details 24 false false R25.htm 100240 - Disclosure - Net Loss Per Share - Schedule of Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureNetLossPerShareScheduleOfOutstandingSharesOfCommonStockEquivalentsExcludedFromCalculationOfDilutedNetLossPerShareDetail Net Loss Per Share - Schedule of Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) Details 25 false false R26.htm 100250 - Disclosure - Net Loss Per Share - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureNetLossPerShareAdditionalInformationDetail Net Loss Per Share - Additional Information (Detail) Details 26 false false R27.htm 100260 - Disclosure - Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsScheduleOfFairValueOfFinancialAssetsMeasuredOnRecurringBasisDetail Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) Details 27 false false R28.htm 100270 - Disclosure - Fair Value Measurements - Summary of Fair Value of Financial Liabilities Assumptions (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFairValueOfFinancialLiabilitiesAssumptionsDetail Fair Value Measurements - Summary of Fair Value of Financial Liabilities Assumptions (Detail) Details 28 false false R29.htm 100280 - Disclosure - Fair Value Measurements - Additonal Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureFairValueMeasurementsAdditonalInformationDetail Fair Value Measurements - Additonal Information (Detail) Details 29 false false R30.htm 100290 - Disclosure - Balance Sheet Components - Summary of Cash and Cash Equivalents (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfCashAndCashEquivalentsDetail Balance Sheet Components - Summary of Cash and Cash Equivalents (Detail) Details 30 false false R31.htm 100300 - Disclosure - Balance Sheet Components - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfReconciliationOfCashCashEquivalentsAndRestrictedCashDetail Balance Sheet Components - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) Details 31 false false R32.htm 100310 - Disclosure - Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfPrepaidExpensesAndOtherCurrentAssetsDetail Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) Details 32 false false R33.htm 100320 - Disclosure - Balance Sheet Components - Summary of Property and Equipment, Net (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfPropertyAndEquipmentNetDetail Balance Sheet Components - Summary of Property and Equipment, Net (Detail) Details 33 false false R34.htm 100330 - Disclosure - Balance Sheet Components - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsAdditionalInformationDetail Balance Sheet Components - Additional Information (Detail) Details 34 false false R35.htm 100340 - Disclosure - Balance Sheet Components - Summary of Accrued and Other Liabilities (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureBalanceSheetComponentsSummaryOfAccruedAndOtherLiabilitiesDetail Balance Sheet Components - Summary of Accrued and Other Liabilities (Detail) Details 35 false false R36.htm 100350 - Disclosure - Leases - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureLeasesAdditionalInformationDetail Leases - Additional Information (Detail) Details 36 false false R37.htm 100360 - Disclosure - Leases - Schedule of Components of Lease Expense and Related Cash Flows (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureLeasesScheduleOfComponentsOfLeaseExpenseAndRelatedCashFlowsDetail Leases - Schedule of Components of Lease Expense and Related Cash Flows (Detail) Details 37 false false R38.htm 100370 - Disclosure - Leases - Schedule of Maturities Lease Liabilities under Leases Agreements (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureLeasesScheduleOfMaturitiesLeaseLiabilitiesUnderLeasesAgreementsDetail Leases - Schedule of Maturities Lease Liabilities under Leases Agreements (Detail) Details 38 false false R39.htm 100390 - Disclosure - Commitments and Contingencies - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetail Commitments and Contingencies - Additional Information (Detail) Details 39 false false R40.htm 100400 - Disclosure - Stockholders' Equity - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockholdersEquityAdditionalInformationDetail Stockholders' Equity - Additional Information (Detail) Details 40 false false R41.htm 100410 - Disclosure - Stockholders' Equity - Schedule of Common Stock Reserved for Issuance (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockholdersEquityScheduleOfCommonStockReservedForIssuanceDetail Stockholders' Equity - Schedule of Common Stock Reserved for Issuance (Detail) Details 41 false false R42.htm 100420 - Disclosure - Stock-Based Compensation - Schedule of Stock-based Compensation Expense for Employees and Non-employees (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensationScheduleOfStockBasedCompensationExpenseForEmployeesAndNonEmployeesDetail Stock-Based Compensation - Schedule of Stock-based Compensation Expense for Employees and Non-employees (Detail) Details 42 false false R43.htm 100430 - Disclosure - Stock-Based Compensation - Schedule of Estimated Grant-date Fair Values of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensationScheduleOfEstimatedGrantDateFairValuesOfStockBasedAwardsUsingBlackScholesOptionPricingModelAssumptionsDetail Stock-Based Compensation - Schedule of Estimated Grant-date Fair Values of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions (Detail) Details 43 false false R44.htm 100440 - Disclosure - Stock-Based Compensation - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetail Stock-Based Compensation - Additional Information (Detail) Details 44 false false R45.htm 100450 - Disclosure - Stock-Based Compensation - Summary of Stock-Based Compensation Activity (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockBasedCompensationActivityDetail Stock-Based Compensation - Summary of Stock-Based Compensation Activity (Detail) Details 45 false false R46.htm 100460 - Disclosure - Income Taxes - Additional Information (Detail) Sheet http://sierraoncology.com/20210930/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetail Income Taxes - Additional Information (Detail) Details 46 false false All Reports Book All Reports srra-10q_20210930.htm srra-20210930.xsd srra-20210930_cal.xml srra-20210930_def.xml srra-20210930_lab.xml srra-20210930_pre.xml srra-ex101_105.htm srra-ex311_9.htm srra-ex312_6.htm srra-ex321_8.htm srra-ex322_7.htm http://fasb.org/srt/2021-01-31 http://fasb.org/us-gaap/2021-01-31 http://xbrl.sec.gov/stpr/2021 http://xbrl.sec.gov/dei/2021 true true