Net Sales Royalty, Percent

No definition available.

Name:	anab_NetSalesRoyaltyPercent
Namespace Prefix:	anab_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue Recognition, Milestone Method, Milestones Achieved During The Period, Amount

+ References

No definition available.

+ Details

Name:	anab_RevenueRecognitionMilestoneMethodMilestonesAchievedDuringThePeriodAmount
Namespace Prefix:	anab_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Revenue Recognition, Multiple-deliverable Arrangements, Upfront Fee Receivable

+ References

No definition available.

+ Details

Name:	anab_RevenueRecognitionMultipleDeliverableArrangementsUpfrontFeeReceivable
Namespace Prefix:	anab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Revenue Recognized, Milestone Method, Milestone Payment Earned, Net Sales above $1 Billion, Percent

+ References

No definition available.

+ Details

Name:	anab_RevenueRecognizedMilestoneMethodMilestonePaymentEarnedNetSalesAbove1BillionPercent
Namespace Prefix:	anab_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue Recognized, Milestone Method, Milestone Payment Earned, Net Sales below $1 Billion, Percent

+ References

No definition available.

+ Details

Name:	anab_RevenueRecognizedMilestoneMethodMilestonePaymentEarnedNetSalesBelow1BillionPercent
Namespace Prefix:	anab_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ProductOrServiceAxis=anab_AnaptysBiogeneratedAntiPD1AntagonistAntibodyTSR042Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=anab_TESAROInc.AndTESARODevelopmentInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=anab_CollaborationAndExclusiveLicenseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Event (Details) - Anti-PD-1 - TESARO - Amendment - USD ($)			9 Months Ended
	Jan. 01, 2021	Oct. 23, 2020	Sep. 30, 2020
Subsequent Event [Line Items]
Milestones achieved, amount			$ 1,100,000,000
Subsequent event
Subsequent Event [Line Items]
Percent of net sales below $1 billion		8.00%
Revenue Recognition, Multiple-deliverable Arrangements, Upfront Fee Receivable		$ 60,000,000.0
Subsequent event \| Forecast
Subsequent Event [Line Items]
Royalty percent on net sales	1.00%
Subsequent event \| Minimum
Subsequent Event [Line Items]
Percent of net sales above $1 billion		12.00%
Subsequent event \| Maximum
Subsequent Event [Line Items]
Percent of net sales above $1 billion		25.00%