Net Loss per Share - Potentially Dilutive Common Stock Equivalent Shares Excluded from Computation of Weighted-Average Shares Outstanding (Detail) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Redeemable convertible preferred stock		8,696
Options outstanding	3,401	3,971
Restricted stock units outstanding	1,419
Unvested restricted shares		58
Warrants	28	47
Total	4,848	12,772