Net Loss per Share - Computation of Denominators Used in Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic:
Weighted average common shares outstanding	35,892,786	31,202,842	27,279,008
Diluted:
Weighted average shares outstanding - Basic	35,892,786	31,202,842	27,279,008
Common stock options	0	0	0
Denominator for diluted net loss per share	35,892,786	31,202,842	27,279,008