3.10.0.1 html 103 201 1 false 40 0 false 6 false false R1.htm 100000 - Document - Document and Entity Information Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DocumentDocumentAndEntityInformation Document and Entity Information Cover 1 false false R2.htm 100010 - Statement - Condensed Consolidated Balance Sheets Sheet http://kezarlifesciences.com/20180630/taxonomy/role/StatementCondensedConsolidatedBalanceSheets Condensed Consolidated Balance Sheets Statements 2 false false R3.htm 100020 - Statement - Condensed Consolidated Balance Sheets (Parenthetical) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsParenthetical Condensed Consolidated Balance Sheets (Parenthetical) Statements 3 false false R4.htm 100030 - Statement - Condensed Consolidated Statements of Operations (Unaudited) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsUnaudited Condensed Consolidated Statements of Operations (Unaudited) Statements 4 false false R5.htm 100040 - Statement - Condensed Consolidated Statements of Comprehensive Loss (Unaudited) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/StatementCondensedConsolidatedStatementsOfComprehensiveLossUnaudited Condensed Consolidated Statements of Comprehensive Loss (Unaudited) Statements 5 false false R6.htm 100050 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited Condensed Consolidated Statements of Cash Flows (Unaudited) Statements 6 false false R7.htm 100060 - Disclosure - Organization and Description of the Business Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureOrganizationAndDescriptionOfBusiness Organization and Description of the Business Notes 7 false false R8.htm 100070 - Disclosure - Summary of Significant Accounting Policies Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies Summary of Significant Accounting Policies Notes 8 false false R9.htm 100080 - Disclosure - Fair Value Measurements Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureFairValueMeasurements Fair Value Measurements Notes 9 false false R10.htm 100090 - Disclosure - Balance Sheet Components Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureBalanceSheetComponents Balance Sheet Components Notes 10 false false R11.htm 100100 - Disclosure - Redeemable Convertible Preferred Stock Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRedeemableConvertiblePreferredStock Redeemable Convertible Preferred Stock Notes 11 false false R12.htm 100110 - Disclosure - Stock-Based Compensation Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensation Stock-Based Compensation Notes 12 false false R13.htm 100120 - Disclosure - Income Taxes Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureIncomeTaxes Income Taxes Notes 13 false false R14.htm 100130 - Disclosure - Net Loss per Share Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureNetLossPerShare Net Loss per Share Notes 14 false false R15.htm 100140 - Disclosure - Related Party Disclosure Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRelatedPartyDisclosure Related Party Disclosure Notes 15 false false R16.htm 100150 - Disclosure - Summary of Significant Accounting Policies (Policies) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies Summary of Significant Accounting Policies (Policies) Policies http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies 16 false false R17.htm 100160 - Disclosure - Summary of Significant Accounting Policies (Tables) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables Summary of Significant Accounting Policies (Tables) Tables http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies 17 false false R18.htm 100170 - Disclosure - Fair Value Measurements (Tables) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureFairValueMeasurementsTables Fair Value Measurements (Tables) Tables http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureFairValueMeasurements 18 false false R19.htm 100180 - Disclosure - Balance Sheet Components (Tables) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureBalanceSheetComponentsTables Balance Sheet Components (Tables) Tables http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureBalanceSheetComponents 19 false false R20.htm 100190 - Disclosure - Redeemable Convertible Preferred Stock (Tables) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRedeemableConvertiblePreferredStockTables Redeemable Convertible Preferred Stock (Tables) Tables http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRedeemableConvertiblePreferredStock 20 false false R21.htm 100200 - Disclosure - Stock-Based Compensation (Tables) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationTables Stock-Based Compensation (Tables) Tables http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensation 21 false false R22.htm 100210 - Disclosure - Net Loss per Share (Tables) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureNetLossPerShareTables Net Loss per Share (Tables) Tables http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureNetLossPerShare 22 false false R23.htm 100220 - Disclosure - Organization and Description of the Business - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureOrganizationAndDescriptionOfBusinessAdditionalInformationDetails Organization and Description of the Business - Additional Information (Details) Details 23 false false R24.htm 100230 - Disclosure - Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfReconciliationOfCashCashEquivalentsAndRestrictedCashDetail Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) Details 24 false false R25.htm 100240 - Disclosure - Fair Value Measurements - Summary of Financial Assets and Liabilities Measured and Recognized at Fair Value on Recurring Basis (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsAndLiabilitiesMeasuredAndRecognizedAtFairValueOnRecurringBasisDetails Fair Value Measurements - Summary of Financial Assets and Liabilities Measured and Recognized at Fair Value on Recurring Basis (Details) Details 25 false false R26.htm 100250 - Disclosure - Fair Value Measurements - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails Fair Value Measurements - Additional Information (Details) Details 26 false false R27.htm 100260 - Disclosure - Fair Value Measurements - Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfAmortizedCostAndEstimatedFairValueOfAvailableForSaleSecuritiesByContractualMaturityDetails Fair Value Measurements - Summary of Amortized Cost and Estimated Fair Value of Available-for-sale Securities by Contractual Maturity (Details) Details 27 false false R28.htm 100270 - Disclosure - Balance Sheet Components - Property and Equipment (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureBalanceSheetComponentsPropertyAndEquipmentDetails Balance Sheet Components - Property and Equipment (Details) Details 28 false false R29.htm 100280 - Disclosure - Balance Sheet Components - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureBalanceSheetComponentsAdditionalInformationDetails Balance Sheet Components - Additional Information (Details) Details 29 false false R30.htm 100290 - Disclosure - Balance Sheet Components - Accrued Liabilities (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureBalanceSheetComponentsAccruedLiabilitiesDetails Balance Sheet Components - Accrued Liabilities (Details) Details 30 false false R31.htm 100300 - Disclosure - Redeemable Convertible Preferred Stock - Schedule of Redeemable Convertible Preferred Stock (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRedeemableConvertiblePreferredStockScheduleOfRedeemableConvertiblePreferredStockDetails Redeemable Convertible Preferred Stock - Schedule of Redeemable Convertible Preferred Stock (Details) Details 31 false false R32.htm 100310 - Disclosure - Redeemable Convertible Preferred Stock - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRedeemableConvertiblePreferredStockAdditionalInformationDetails Redeemable Convertible Preferred Stock - Additional Information (Details) Details 32 false false R33.htm 100320 - Disclosure - Stock-Based Compensation - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails Stock-Based Compensation - Additional Information (Details) Details 33 false false R34.htm 100330 - Disclosure - Stock-Based Compensation - Summary of Activity under Stock Option Plan and Related Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationSummaryOfActivityUnderStockOptionPlanAndRelatedInformationDetails Stock-Based Compensation - Summary of Activity under Stock Option Plan and Related Information (Details) Details 34 false false R35.htm 100340 - Disclosure - Stock-Based Compensation - Summarizes of Activity of Nonvested Restricted Stock (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationSummarizesOfActivityOfNonvestedRestrictedStockDetails Stock-Based Compensation - Summarizes of Activity of Nonvested Restricted Stock (Details) Details 35 false false R36.htm 100350 - Disclosure - Stock-Based Compensation - Stock-Based Compensation Recognized (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationStockBasedCompensationRecognizedDetails Stock-Based Compensation - Stock-Based Compensation Recognized (Details) Details 36 false false R37.htm 100360 - Disclosure - Stock-Based Compensation - Unrecognized Stock-based Compensation Cost and Estimated Weighted Average Amortization Period (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationUnrecognizedStockBasedCompensationCostAndEstimatedWeightedAverageAmortizationPeriodDetails Stock-Based Compensation - Unrecognized Stock-based Compensation Cost and Estimated Weighted Average Amortization Period (Details) Details 37 false false R38.htm 100370 - Disclosure - Stock-Based Compensation - Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureStockBasedCompensationFairValueOfEmployeeStockOptionsGrantedIsCalculatedUsingBlackScholesOptionPricingModelWithWeightedAverageAssumptionsDetails Stock-Based Compensation - Fair Value of Employee Stock Options Granted is Calculated Using Black Scholes Option Pricing Model with Weighted Average Assumptions (Details) Details 38 false false R39.htm 100380 - Disclosure - Income Taxes - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails Income Taxes - Additional Information (Details) Details 39 false false R40.htm 100390 - Disclosure - Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureNetLossPerShareCalculationOfBasicAndDilutedNetLossPerShareDetails Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details) Details 40 false false R41.htm 100400 - Disclosure - Net Loss Per Share - Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureNetLossPerShareAntiDilutiveOutstandingSharesOfCommonStockEquivalentsExcludedFromComputationOfDilutedNetLossPerShareDetails Net Loss Per Share - Anti-dilutive Outstanding Shares of Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Details) Details 41 false false R42.htm 100410 - Disclosure - Related Party Disclosure - Additional Information (Details) Sheet http://kezarlifesciences.com/20180630/taxonomy/role/DisclosureRelatedPartyDisclosureAdditionalInformationDetails Related Party Disclosure - Additional Information (Details) Details 42 false false All Reports Book All Reports kzr-20180630.xml kzr-20180630.xsd kzr-20180630_cal.xml kzr-20180630_def.xml kzr-20180630_lab.xml kzr-20180630_pre.xml http://fasb.org/us-gaap/2018-01-31 http://xbrl.sec.gov/dei/2018-01-31 http://fasb.org/srt/2018-01-31 true true