Summary of Unvested Stock Option Activity (Detail) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Weighted Average Grant Date Fair Value
Granted	$ 0.54	$ 1.53
Stock Options
Shares
Beginning Balance	254
Granted	20
Vested	(47)
Forfeited or cancelled	(14)
Ending Balance	213
Weighted Average Grant Date Fair Value
Beginning Balance	$ 1.44
Granted	0.54
Vested	1.63
Forfeited or cancelled	2.61
Ending Balance	$ 1.25