Collaborative Research and Development Agreements (Details)	1 Months Ended		3 Months Ended								12 Months Ended
	Nov. 30, 2014 USD ($) target	Mar. 31, 2014 USD ($) target	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) milestone	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2011 USD ($)
Deferred Revenue Arrangement [Line Items]
Collaboration revenue											$ 10,000,000	$ 16,684,000	$ 17,571,000
TESARO | Collaborative Research and Development Agreement
Deferred Revenue Arrangement [Line Items]
Upfront license fee received	$ 2,000,000	$ 17,000,000
Number of outstanding research and development targets | target	4	3
Milestone payments, contingent upon preclinical and clinical trial events (up to)	$ 18,000,000
Milestone payments, contingent upon certain U.S. and European regulatory submissions and approvals (up to)	90,000,000
Milestone payments, contingent upon achievement of specified levels of worldwide sales (up to)	$ 165,000,000
Agreement term following first commercial sale or expiration of the last to expire patent (in years)	12 years
Collaboration revenue											$ 10,000,000	15,200,000	17,600,000
Number of milestones achieved during period | milestone											3
Milestone method, revenue recognized												9,300,000	1,700,000
Revenue recognized, funding for research and development services												3,200,000	6,500,000
Amortization of upfront fee												2,600,000	9,400,000
TESARO | In Vivo Toxicology Studies Using GLPs | AnaptysBio Generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount										$ 1,000,000
TESARO | In Vivo Toxicology Studies Using GLPs | AnaptysBio Generated Anti-TIM3 Antagonist Antibody (TSR-022)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount									$ 1,000,000
TESARO | In Vivo Toxicology Studies Using GLPs | AnaptysBio Generated Anti-LAG3 Antagonist Antibody (TSR-033)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount						$ 1,000,000
TESARO | IND clearance from the FDA | AnaptysBio Generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount								$ 4,000,000
TESARO | IND clearance from the FDA | AnaptysBio Generated Anti-TIM3 Antagonist Antibody (TSR-022)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount							$ 4,000,000
TESARO | IND clearance from the FDA | AnaptysBio Generated Anti-LAG3 Antagonist Antibody (TSR-033)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount				$ 4,000,000
TESARO | Phase 2 clinical trial initiation | AnaptysBio Generated Anti-PD-1 Antagonist Antibody (TSR-042)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount				$ 3,000,000
TESARO | Phase 2 clinical trial initiation | AnaptysBio Generated Anti-TIM3 Antagonist Antibody (TSR-022)
Deferred Revenue Arrangement [Line Items]
Milestones achieved during period, amount			$ 3,000,000
Celgene Corporation | Collaborative Research and Development Agreement
Deferred Revenue Arrangement [Line Items]
Upfront license fee received														$ 6,000,000
Collaboration revenue											$ 0	$ 1,500,000	$ 0
Maximum milestone payments per target														$ 53,000,000
Celgene Corporation | In Vivo Toxicology Studies Using GLPs | AnaptysBio Generated Anti-PD-1 (CC-90006)
Deferred Revenue Arrangement [Line Items]
Milestone payment earned							$ 500,000
Celgene Corporation | Phase 1 clinical trial initiation | AnaptysBio Generated Anti-PD-1 (CC-90006)
Deferred Revenue Arrangement [Line Items]
Milestone payment earned					$ 1,000,000