Summary of Status of Unvested Options and Changes in Number of Shares Subject to and in Weighted Average Grant Date Fair Values of Unvested Options (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012
Unvested Options
Unvested, Beginning of Period	352,049
Granted	421,500
Vested	(105,111)
Forfeited/Cancelled	(27,490)
Unvested, End of Period	640,948
Weighted Average Grant Date Fair Value
Unvested, Beginning Balance	$ 1.39
Granted	$ 2.34
Vested	$ 1.47
Forfeited/Cancelled	$ 2.99
Unvested, End of Period	$ 1.99