Stockholders' Equity - Summary of Non-Vested Stock Options (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Nonvested at beginning of period	829,431
Nonvested, Shares, Granted	960,175
Nonvested, Shares, Vested	(363,701)
Nonvested, Shares, Forfeited	(540,421)
Nonvested at end of period	885,484
Weighted Average Grant Date Fair Value, Nonvested at December 31, 2017 | $ / shares	$ 2.70
Nonvested at December 31, 2017, Aggregate Intrinsic Value | $	$ 629