Stock Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 3,466,000	$ 3,290,000	$ 3,106,000
Common stock reserved	19,700,000
Shares reserved for future issuance	17,061,260
Maximum term of options granted	10 years
Number of options to be granted to any one individual	1,300,000
Percentage of options vested annually	25.00%
Number of underlying shares exercisable	5,212,897	5,031,587	3,895,520
Weighted average exercise price of options exercisable	$ 3.49	$ 3.55	$ 4.26
Weighted average remaining contractual term of options outstanding	6 years
Weighted average remaining contractual term of options exercisable	4 years 3 months 18 days
Weighted average remaining contractual term of vested and unvested options expected to vest	5 years 10 months 24 days
Aggregate intrinsic value of options outstanding	0
Aggregate intrinsic value of options exercisable	0
Unrecognized compensation cost related to unvested options	2,300,000
Unvested stock-based awards expected to be recognized, weighted-average period	1 year 3 months 22 days
Weighted average grant-date fair value of options granted	$ 1.31	$ 1.88	$ 1.21
Total intrinsic value of options exercised	500,000	100,000	100,000
Shares available for grant	7,871,325
Aggregate grant-date fair value of RSUs vested	1,000,000	1,100,000	1,000,000
Common stock underlying RSUs that were fully vested	289,350
Restricted stock units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1,000,000	800,000	1,100,000
Aggregate RSUs granted	409,189	258,456	545,780
Percentage of options vested	25.00%
Unvested stock-based awards expected to be recognized, weighted-average period	1 year 3 months 11 days
Aggregate grant-date fair value of RSUs granted	1,000,000	900,000	1,300,000
Total unrecognized compensation cost related to unvested RSUs	$ 600,000