Net Income (Loss) Per Share Attributable to Common Stockholders (Details 1)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Potentially dilutive securities not included in the calculation of diluted net income (loss) per share
Total potentially dilutive securities	39,232,162	98,473,622	39,232,162	92,540,254
Common stock options [Member]
Potentially dilutive securities not included in the calculation of diluted net income (loss) per share
Total potentially dilutive securities	37,279,442	14,246,439	37,279,442	8,548,888
Convertible preferred stock [Member]
Potentially dilutive securities not included in the calculation of diluted net income (loss) per share
Total potentially dilutive securities		83,703,016		83,703,016
RSUs [Member]
Potentially dilutive securities not included in the calculation of diluted net income (loss) per share
Total potentially dilutive securities	1,134,851		1,134,851
Common stock subject to repurchase [Member]
Potentially dilutive securities not included in the calculation of diluted net income (loss) per share
Total potentially dilutive securities	349,165	524,167	349,165	288,350
ESPP obligations [Member]
Potentially dilutive securities not included in the calculation of diluted net income (loss) per share
Total potentially dilutive securities	468,704		468,704