Activity of Outstanding Stock Options (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Number of Shares
Beginning Balance	2,170,043
Granted	81,200
Cancelled / Forfeited	(170,829)
Ending Balance	2,080,414
Vested and exercisable at June 30, 2013	1,486,472
Expected to vest as of June 30, 2013	2,027,145
Weighted Average Remaining Contractual term
Balance, June 30, 2013	6 years 4 months 24 days
Vested and exercisable at June 30, 2013	5 years 8 months 12 days
Expected to vest as of June 30, 2013	6 years 3 months 18 days
Aggregate Intrinsic Value
Balance, June 30, 2013
Vested and exercisable at June 30, 2013
Expected to vest as of June 30, 2013
Balance, January 1, 2013
Number of Shares
Price range, lower limit	$ 1.49
Price range, upper limit	$ 4.65
Granted
Number of Shares
Price range, lower limit	$ 1.19
Price range, upper limit	$ 1.19
Cancelled / Forfeited
Number of Shares
Price range, lower limit	$ 1.19
Price range, upper limit	$ 4.65
Balance, June 30, 2013
Number of Shares
Price range, lower limit	$ 1.19
Price range, upper limit	$ 4.65
Expected to vest as of June 30, 2013
Number of Shares
Price range, lower limit	$ 1.49
Price range, upper limit	$ 4.65
Expected to vest as of June 30, 2013
Number of Shares
Price range, lower limit	$ 1.19
Price range, upper limit	$ 4.65