Business - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended					3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Oct. 31, 2015	Sep. 30, 2015	Aug. 31, 2015	Aug. 31, 2014	Apr. 30, 2013	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2012	Dec. 31, 2015
Nature Of Business [Line Items]
Date of formation									Jul. 02, 2004
Proceeds from equity and debt financing	$ 204,800
Upfront and milestone payments received in connection with license agreements	32,500
Unrestricted cash and cash equivalents and marketable securities	84,764						$ 84,764		$ 84,764
Accumulated deficit	$ 128,657						128,657		128,657			$ 104,891
Net loss							$ 13,075	$ 5,684	23,766	$ 10,373
Net cash used in operating activities									$ 21,292	$ 9,495
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			$ 1,725		$ 480
Chong Kun Dang Pharmaceutical Corporation [Member]
Nature Of Business [Line Items]
Milestone payment received		$ 417		$ 209
Upfront and milestone payments related to license agreement											$ 1,190