Summary of Information Regarding Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2010
Options Outstanding
Options outstanding at December 31, 2011	2,823,400		2,566,450
Granted	368,690
Exercised	(609,400)
Forfeited/cancelled	(267,600)
Options outstanding at December 31, 2012	2,315,090		2,566,450
Options exercisable at December 31, 2012	1,447,600
Vested and expected to vest at December 31, 2012	2,186,609	[1]
Weighted average exercise price per share
Options outstanding at December 31, 2011	$ 4.05		$ 4.08
Granted	$ 3.65
Exercised	$ 3.06
Forfeited/cancelled	$ 4.44
Options outstanding at December 31, 2012	$ 4.20		$ 4.08
Options exercisable at December 31, 2012	$ 4.39
Vested and expected to vest at December 31, 2012	$ 4.21	[1]
Weighted average remaining contractual term (in years)
Options outstanding at December 31, 2012	6 years 1 month 28 days
Options exercisable at December 31, 2012	4 years 11 months 16 days
Vested and expected to vest at December 31, 2012	6 years 18 days	[1]
Aggregate intrinsic value
Options outstanding at December 31, 2012	$ 4,854,412
Options exercisable at December 31, 2012	2,783,183
Vested and expected to vest at December 31, 2012	$ 4,570,615	[1]

[1] This represents the number of vested options as of December 31, 2012 plus the number of unvested options expected to vest as of December 31, 2012 based on the unvested outstanding options at December 31, 2012 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.