Business - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended						3 Months Ended								12 Months Ended
	Dec. 31, 2015	Oct. 31, 2015	Sep. 30, 2015	Aug. 31, 2015	Aug. 31, 2014	Apr. 30, 2013	Apr. 30, 2012	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Nature Of Business [Line Items]
Date of formation																Jul. 02, 2004
Proceeds from equity and debt financing	$ 204,800
Upfront and milestone payments earned in connection with license agreements	32,500
Upfront and milestone payments related to license agreement																$ 1,710	$ 302	$ 9,637
Unrestricted cash and cash equivalents and marketable securities	106,740							$ 106,740								106,740
Accumulated deficit	$ 104,891							104,891				$ 80,201				104,891	80,201
Net loss								$ 9,530	$ 4,787	$ 5,684	$ 4,689	$ 4,172	$ 6,545	$ 3,645	$ 3,383	24,690	17,745	3,963
Net cash used in operating activities																$ (21,478)	$ (17,642)	$ 2,829
Minimum [Member]
Nature Of Business [Line Items]
Expected period to fund operations																1 year
Maruishi Pharmaceutical Co., Ltd. [Member]
Nature Of Business [Line Items]
Upfront license fee received						$ 15,000
Milestone payment received					$ 480
Amount due from milestone payments net of contractual foreign currency exchange adjustments			$ 1,725
Upfront and milestone payments related to license agreement																$ 1,084
Chong Kun Dang Pharmaceutical Corporation [Member]
Nature Of Business [Line Items]
Milestone payment received		$ 417		$ 209
Upfront and milestone payments related to license agreement							$ 646												$ 1,190