Collaborations - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended							12 Months Ended
	Oct. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Aug. 31, 2015 USD ($)	Aug. 31, 2014 USD ($)	Jun. 30, 2014 USD ($)	Apr. 30, 2013 USD ($) $ / shares shares	Apr. 30, 2012 USD ($) shares	Dec. 31, 2015 USD ($) Deliverables shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares	Dec. 31, 2012 USD ($) shares	Feb. 05, 2014 shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and milestone fee revenue								$ 1,710	$ 302	$ 9,637
Deferred R&D service revenue									1,452
Collaborative revenue								2,093	2,201	2,225
Clinical compound revenue								$ 0	$ 674	$ 102
Issuance of convertible preferred stock | shares								0	0	29,186,929	26,636,118	29,186,929
Research and development expense								$ 21,221	$ 15,068	$ 8,685
Junior Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of convertible preferred stock | shares										173,611	173,611
Junior A Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of convertible preferred stock | shares										2,105,263
Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront non-refundable, non-creditable license fee						$ 15,000
License and milestone fee revenue								$ 1,084
Milestone payment received				$ 480
Number of deliverables for revenue recognized | Deliverables								2
Value of arrangement						15,337
Deferred R&D service revenue								$ 0	1,452
Revenue recognized from nonsubstantive milestones								8,000
Revenue recognized from substantive milestones								2,500
Non-refundable contingent payment					$ 480
Collaborative revenue								641
Amount due from milestone payments net of contractual foreign currency exchange adjustments		$ 1,725
Contractual foreign currency exchange adjustments		$ 275
Stock purchase agreement, purchase price of preferred stock						8,000
Stock purchase agreement, purchase price fair value of preferred stock						$ 7,663
Stock purchase agreement, purchase price fair value of preferred stock per share | $ / shares						$ 3.64
Stock purchase agreement, purchase price premium of preferred stock						$ 337
Clinical trial costs related to the R&D services deliverable								1,583	3,000	$ 2,420
Research and development expense									3,558	2,452
Cost of clinical compound sold to Maruishi									$ 558	$ 32
Maruishi Pharmaceutical Co., Ltd. [Member] | Junior A Convertible Preferred Stock [Member] | Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of convertible preferred stock | shares						2,105,263
Stock purchase agreement, purchase price of preferred stock per share | $ / shares						$ 3.80
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Next potential milestone that could be received								1,000
Maruishi Pharmaceutical Co., Ltd. [Member] | License [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and milestone fee revenue					302	$ 9,637
Estimated selling price						10,200
Maruishi Pharmaceutical Co., Ltd. [Member] | R & D Services [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated selling price						6,200
Deferred R&D service revenue					90	$ 5,700
Collaborative revenue					$ 88
Chong Kun Dang Pharmaceutical Corporation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront non-refundable, non-creditable license fee							$ 1,000
Milestone payments receivable							3,750
License and milestone fee revenue							$ 646				$ 1,190
Milestone payment received	$ 417		$ 209
South Korean Withholding tax	$ 83		$ 41
Next potential milestone that could be received								$ 750
Chong Kun Dang Pharmaceutical Corporation [Member] | Junior Convertible Preferred Stock [Member] | Convertible Preferred Stock [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of convertible preferred stock, Shares | shares							173,611
Issuance of convertible preferred stock, Value							$ 354
Chong Kun Dang Pharmaceutical Corporation [Member] | Clinical Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable							2,250
Chong Kun Dang Pharmaceutical Corporation [Member] | Regulatory Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable							$ 1,500