Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding at beginning of period	3,468,991	3,397,529	3,196,100
Number of Shares, Granted	960,175
Number of Shares, Exercised	(202,519)	(147,425)	(235,480)
Number of Shares, Forfeitures	(1,510,193)	(434,486)	(247,720)
Number of Shares, Outstanding at end of period	2,712,954	3,468,991	3,397,529
Weighted Average Exercise Price Per Share, Outstanding at beginning of period	$ 4.14	$ 5.42	$ 4.32
Weighted average Exercise Price Per Share, Exercised	2.17	2.01	3.52
Weighted Average Exercise Price Per Share, Forfeitures	5.13	13.17	12.65
Weighted Average Exercise Price Per Share, Outstanding at end of period	$ 2.98	$ 4.14	$ 5.42
Aggregate Intrinsic Value, Outstanding at beginning of period	$ 0	$ 3,124	$ 22,881
Aggregate Intrinsic Value, Granted	$ 0	$ 0	$ 0
Aggregate Intrinsic Value, Outstanding at end of period	$ 1,190	$ 0	$ 3,124
Officers and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted	83,658	95,000
Weighted Average Exercise Price Per Share, Granted	$ 2.64	$ 2.34
Others [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted	873,017	558,373	684,629
Weighted Average Exercise Price Per Share, Granted	$ 1.96	$ 3.12	$ 8.14