Collaboration Agreements - Additional Information (Detail) $ / shares in Units, shares in Millions	1 Months Ended		3 Months Ended		7 Months Ended	9 Months Ended		12 Months Ended	34 Months Ended
	Aug. 31, 2017 USD ($) employee $ / shares shares	Mar. 31, 2014 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under collaboration agreement			$ 10,101,000	$ 4,766,000		$ 28,682,000	$ 12,466,000
Estimated deferred revenue recognized within one year			16,678,000			16,678,000		$ 19,033,000	$ 19,033,000
Merck Sharp & Dohme Corp. | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from Collaborators						12,000,000
Collaborative Arrangement | Celgene Corporation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments		$ 17,000,000
Minimum annual revenue period		3 years
Deferred revenue recorded under collaboration agreement			5,100,000			5,100,000
Estimated deferred revenue recognized within one year			2,800,000			$ 2,800,000
Collaborative agreement period						1 year
License and Services Revenue			(100,000)	600,000		$ 500,000	2,300,000
Collaborative Arrangement | Celgene Corporation | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum success-based milestone payments		$ 45,000,000
Collaborative Arrangement | Celgene Corporation | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement upfront payment		$ 5,800,000							$ 2,100,000
Proceeds from Collaborators								6,000,000
Collaborative Arrangement | Merck Sharp & Dohme Corp.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recorded under collaboration agreement			12,100,000			12,100,000
Proceeds from Collaborators			2,300,000	1,900,000		5,600,000	5,700,000
Collaborative Arrangement | Merck Sharp & Dohme Corp. | Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from Collaborators					$ 3,900,000			12,000,000
License and Services Revenue								$ 8,500,000
Collaborative Arrangement | Medivation, Inc. and Astellas Pharma, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized under collaboration agreement							0
License and Services Revenue			300,000	1,500,000		11,500,000	3,600,000
Gain (Loss) on Contract Termination			1,000,000
Collaborative Arrangement | Lam Research Corporation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Other Liabilities, Current			8,000,000			8,000,000
Proceeds from Collaborators			9,200,000			9,200,000
License and Services Revenue			900,000			900,000
Exercise Price Of Common Stock Warrants | $ / shares	$ 16.75
Stock and Warrants Issued During Period, Value, Preferred Stock and Warrants	$ 6,700,000
Maximum Amount Of Royalties Payable, Ratio To License And Service Revenue	3
Reimbursement Of Counterparty Costs, Maximum Number Of Employees | employee	10
Collaborative Arrangement | Lam Research Corporation | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and Services Revenue	$ 50,000,000
Class of Warrant or Right, Outstanding | shares	1.0
Clinical Research Collaborative Arrangement | Merck Sharp & Dohme Corp.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated deferred revenue recognized within one year			10,000,000			$ 10,000,000
Collaborative agreement period						1 year
License and Services Revenue			$ 8,800,000	$ 2,200,000		$ 15,400,000	$ 6,100,000