Common Stock Reserved for Issuance (Details) (USD $)	0 Months Ended	9 Months Ended
	Jun. 06, 2014	Sep. 30, 2014		Sep. 30, 2013	Jun. 06, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		27,077,000				48,137,000
Ratio of shares issued upon conversion					1
Repayment of Notes Payable and Accrued Interest	$ 23,600,000
Repayment on notes payable		20,000,000		0
Withholding taxes	1,100,000
Converted debt amount	$ 96,500,000
Conversion of convertible preferred stock outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		0	[1]			24,000,000	[1]
Outstanding stock options and RSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		13,977,000				11,245,000
Outstanding stock purchase rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		2,000				2,000
Convertible notes payable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		0	[2]			3,949,000	[2]
Shares reserved for future option and RSA grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		12,447,000				8,941,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)		651,000				0
Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon conversion	24,000,000
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon conversion	24,000,000
Ratio of shares issued upon conversion					1
Issue price (usd per share)					$ 43
Convertible notes payable | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon conversion	2,200,000

[1] Upon the closing of our IPO, all shares of our convertible preferred stock were converted to 24 million shares of common stock on a one-for-one basis.

[2] Upon the closing of our IPO, all noteholders with the exception of one noteholder converted the principal and accrued interest amount outstanding under their subordinated convertible promissory notes into shares of our common stock at the IPO price of $43.00 per share. The noteholder, who did not elect to so convert, was paid a total of $23.6 million which included principal and accrued interest less applicable withholding taxes of $1.1 million. The remainder of the noteholders converted the remaining debt balance of approximately $96.5 million including principal and accrued interest into 2.2 million shares of our common stock.