Net Loss per Share - Computation of Denominators Used in Net Loss per Share (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic:
Weighted average common shares outstanding	38,034,216	32,591,550	34,696,835	30,729,752
Diluted:
Weighted average common shares outstanding - Basic	38,034,216	32,591,550	34,696,835	30,729,752
Common stock options	0	0	0	0
Denominator for diluted net loss per share	38,034,216	32,591,550	34,696,835	30,729,752