Stock Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,902	$ 3,159	$ 3,466
Common stock reserved	19,700,000
Shares reserved for future issuance	16,448,052
Maximum term of options granted	10 years
Number of options to be granted to any one individual	1,300,000
Number of underlying shares exercisable	6,884,679	6,037,169	5,212,897
Weighted average exercise price of options exercisable	$ 2.68	$ 2.89	$ 3.49
Weighted average remaining contractual term of options outstanding	6 years 3 months 18 days
Weighted average remaining contractual term of options exercisable	5 years 6 months
Weighted average remaining contractual term of vested and unvested options expected to vest	6 years 3 months 18 days
Aggregate intrinsic value of options outstanding	$ 0
Aggregate intrinsic value of options exercisable	0
Unrecognized compensation cost related to unvested options	$ 800
Unvested stock-based awards expected to be recognized, weighted-average period	1 year 4 months 2 days
Weighted average grant-date fair value of options granted	$ 0.51	$ 0.73	$ 1.31
Number of options exercised	0	0	347,450
Total intrinsic value of options exercised			$ 500
Shares available for grant	5,421,917
Aggregate grant-date fair value of RSUs vested	$ 1,000	$ 800	1,000
Common stock underlying RSUs that were fully vested	529,555
Restricted stock units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 800	$ 1,100	$ 1,000
Aggregate RSUs granted	788,429	828,000	409,189
Unvested stock-based awards expected to be recognized, weighted-average period	1 year 4 months 6 days
Aggregate grant-date fair value of RSUs granted	$ 800	$ 1,200	$ 1,000
Total unrecognized compensation cost related to unvested RSUs	$ 500
Share-based Compensation Award, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of options vested	25.00%
Share-based Compensation Award, Tranche One [Member] | Restricted stock units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of options vested	25.00%