Net Loss Per Share - Potentially Dilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	65,081	64,330
Options to purchase common stock
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	22,274	22,538
Shares subject to repurchase
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	52	37
Restricted stock units
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	2,255	1,255
Note Hedge Warrants
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	20,250	20,250
Convertible Debt Securities (2020 Notes)
Potentially dilutive securities
Total potentially dilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)	20,250	20,250