Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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
Operating expenses
Research and development	$ 6,293	$ 6,092	$ 6,616	$ 5,671	$ 3,907	$ 3,511	$ 3,094	$ 1,669	$ 24,672	$ 12,181	$ 12,413
General and administrative	2,774	2,826	3,119	2,152	5,086	12	1,873	869	10,871	7,840	2,764
Impairment of intangible assets		17,315							17,315
Total operating expenses	9,067	26,233	9,735	7,823	8,993	3,523	4,967	2,538	52,858	20,021	15,177
Net loss and comprehensive loss	$ (9,387)	$ (22,211)	$ (10,987)	$ (7,032)	$ (10,414)	$ (2,940)	$ (7,916)	$ (2,830)	$ (49,617)	$ (24,100)	$ (18,589)
Net loss per share, basic and diluted	$ (0.50)	$ (1.22)	$ (0.99)	$ (17.43)	$ (25.81)	$ (7.29)	$ (19.62)	$ (7.01)	$ (4.08)	$ (59.72)	$ (47.31)