Stockholders' Equity - Summary of Non-Vested Stock Options (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Nonvested at beginning of period	885,484
Nonvested, Shares, Granted	2,549,177
Nonvested, Shares, Vested	(209,500)
Nonvested, Shares, Forfeited	(461,328)
Nonvested at end of period	2,763,833
Weighted Average Grant Date Fair Value, Nonvested at December 31, 2018 | $ / shares	$ 1.54
Nonvested at December 31, 2018 ,Aggregate Intrinsic Value | $	$ 5,979