Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 10, 2014	Nov. 06, 2012	Apr. 30, 2015	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2015
Accounting Policies [Abstract]
Company milestone-based grant	$ 12,600	$ 8,300
Fund received for research and development activities		$ 2,600
Milestone payments received	$ 10,600		$ 2,400			$ 2,500
Company's expectation to receive milestone payment in 2016				$ 2,800
Company grant revenue				1,700	$ 1,200
Restricted cash				0			$ 63
Deferred grant revenue				$ 1,912			$ 3,658