Liquidity - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liquidity And Managements Plans [Line Items]
Cash	$ 21,195	$ 32,019	$ 83,560	$ 70,472
Net cash flows from operating activities	(32,451)	(53,982)	(3,732)
Stockholders' equity (deficit)	8,877	$ (17,665)	$ 31,696	$ 54,396
CRG [Member] | Line of Credit [Member]
Liquidity And Managements Plans [Line Items]
Additional borrowing capacity	$ 15,000