Net Loss Per Share Attributable To Common Stockholders - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Options exercised to purchase common stock (in shares)	907,000
Stock Repurchase Plan
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Exercisable options to purchase common stock (in number of options)	75,000
Options exercised to purchase common stock (in shares)			60,000
Option outstanding, un-vested and subject to repurchase right (in number of options)	15,000	35,000