Collaboration and License Agreements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 3,828,000	$ 9,322,000	$ 12,743,000	$ 21,811,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	1,038,000	1,798,000	3,824,000	4,785,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments eligible for achievement	0
Collaboration and license revenue	400,000	600,000	1,400,000	1,600,000
Deferred revenue	9,800,000		9,800,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	600,000	1,200,000	2,400,000	3,200,000
Deferred revenue	8,200,000		8,200,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | 2016 Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment receivable upon the achievement of certain regulatory events	20,000,000
Payment receivable upon the achievement of annual net sales volumes	$ 70,000,000
Percentage of royalties entitle to receive under agreement	15.00%
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | 2016 Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalties entitle to receive under agreement	5.00%
Daiichi Sankyo, Inc ("Daiichi")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 2,034,000	3,810,000	6,227,000	8,491,000
Daiichi Sankyo, Inc ("Daiichi") | 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	1,800,000	3,400,000	5,400,000	7,700,000
Deferred revenue	7,200,000		7,200,000
Milestone payments of regulatory clinical event and patient enrollment targets			12,500,000
Contingent and non-contingent consideration to be recognized after resolution of contingency			8,000,000
Daiichi Sankyo, Inc ("Daiichi") | 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	200,000	400,000	900,000	800,000
Deferred revenue	2,900,000		2,900,000
Daiichi Sankyo, Inc ("Daiichi") | 2016 Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments eligible for achievement of initial and final regulatory approval	10,000,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	544,000	3,316,000	1,880,000	7,431,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	500,000	3,300,000	1,900,000	7,400,000
Deferred revenue	2,200,000		2,200,000
Milestone payments eligible for achievement of certain events	5,000,000
Bayer Pharma AG
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	212,000	398,000	812,000	1,052,000
Bayer Pharma AG | 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	200,000	$ 400,000	800,000	$ 1,100,000
Deferred revenue	$ 2,700,000		2,700,000
Milestone payment associated with regulatory approval			$ 10,000,000