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Collaborations - Additional Information (Detail) $ in Thousands	1 Months Ended				12 Months Ended
	Sep. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Apr. 30, 2013 USD ($)	Apr. 30, 2012 USD ($)	Dec. 31, 2017 USD ($) Deliverable	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and milestone fee revenue					$ 530		$ 1,710
Withholding tax					(204)	$ (468)	(397)
Collaborative revenue					313		2,093
Clinical compound revenue					68	86
Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and milestone fee revenue		$ 480			530		1,084
Upfront non-refundable, non-creditable license fee			$ 15,000		$ 843
Number of deliverables for revenue recognized \| Deliverable					2
Revenue recognized from non-substantive milestones					$ 8,000
Revenue recognized from substantive milestones					2,500
Contractual foreign currency exchange adjustments	$ 275	20
Collaborative revenue					313		641
Amount due from milestone payments net of contractual foreign currency exchange adjustments	$ 1,725
Clinical compound revenue					68	86	0
Cost of clinical compound related to R&D expense					61	$ 78
Clinical trial costs related to the R&D services deliverable							1,583
Chong Kun Dang Pharmaceutical Corporation [Member] \| South Korea
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Withholding tax							124
Clinical Development [Member] \| United States [Member] \| Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Next potential milestone that could be received					1,000
Clinical Development [Member] \| Japan [Member] \| Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Next potential milestone that could be received					$ 2,000
License [Member] \| Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and milestone fee revenue		302
Estimated selling price			10,200
R & D Services [Member] \| Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Estimated selling price			$ 6,200
Collaborative revenue		88
Deferred R&D service revenue		$ 90
Supply Agreement [Member] \| Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Price to be paid as percentage of fully burdened manufacturing cost					110.00%
Chong Kun Dang Pharmaceutical Agreement [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							626
Next potential milestone that could be received							$ 750
Chong Kun Dang Pharmaceutical Agreement [Member] \| Clinical Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable				2,250
Chong Kun Dang Pharmaceutical Agreement [Member] \| Regulatory Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable				$ 1,500