Collaboration and License Agreements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 3,787,000	$ 4,231,000	$ 8,915,000	$ 12,489,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	1,027,000	1,733,000	2,785,000	2,987,000
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	1,000,000	1,000,000
Deferred revenue	10,200,000		10,200,000
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	1,800,000	2,000,000
Deferred revenue	8,900,000		8,900,000
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	$ 2,012,000	1,297,000	4,194,000	4,681,000
Daiichi Sankyo, Inc ("Daiichi") | 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	1,800,000	900,000	3,600,000	4,300,000
Deferred revenue	9,000,000		9,000,000
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	600,000	400,000
Deferred revenue	3,100,000		3,100,000
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	538,000	807,000	1,336,000	4,115,000
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	800,000	1,300,000	4,100,000
Deferred revenue	2,700,000		2,700,000
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	210,000	394,000	600,000	654,000
Bayer Pharma AG | 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	200,000	$ 400,000	600,000	$ 700,000
Deferred revenue	$ 3,000,000		3,000,000
Milestone payment associated with regulatory approval			$ 10,000,000