Net Income Per Share Available to Common Stock - Basic and Diluted Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 24,492	$ 12,329
Less: undistributed earnings allocated to participating securities	(460)	(5,967)
Net income attributable to common stockholders, basic	24,032	6,362
Add: undistributed earnings allocated to participating securities	39	454
Net income attributable to common stockholders, diluted	$ 24,071	$ 6,816
Weighted-average shares used in computing net income per share available to common stockholders, basic (in shares)	64,635	29,124
Add weighted-average effect of dilutive securities:
Stock options and RSAs (in shares)	5,928	4,692
Incremental Common Shares Attributable to Dilutive Effect of Employee Stock Purchase Plan	159	0
Weighted-average shares used in computing net income per share available to common stockholders, diluted (in shares)	70,722	33,816
Net income per share attributable to common stockholders:
Basic (usd per share)	$ 0.37	$ 0.22
Diluted (usd per share)	$ 0.34	$ 0.20