Stock Option Activity Under Stock Option Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Number of Shares
Beginning Balance			5,277,085
Granted	140,000	300,500	1,835,755	506,000
Exercised			(482,500)
Cancelled			(1,634,791)
Ending Balance	4,995,549		4,995,549		5,277,085
Options exercisable, at end of period	2,581,327		2,581,327		3,099,935
Options available for future grant	3,971,940		3,971,940
Weighted Average Exercise Price
Beginning Balance			$ 4.24
Granted			2.69
Exercised			3.48
Cancelled			4.11
Ending Balance	$ 3.78		3.78		$ 4.24
Options exercisable, at end of period	$ 4.59		$ 4.59		$ 5.15
Weighted Average Contractual Term (Years)
Outstanding, at end of period			7 years 10 months 2 days
Options exercisable, at end of period			6 years 7 months 6 days		4 years 11 months 4 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 6,025		$ 6,025
Options exercisable, at end of period	$ 2,425		$ 2,425		$ 88