Stock-Based Compensation (Details) (Stock options, USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Stock options
Stock-Based Compensation
Shares available for issuance	605,722
Shares
Options Outstanding at beginning of the period (in shares)	7,015,350
Granted (in shares)	70,650
Exercised (in shares)	(545,867)
Canceled (in shares)	(1,213)
Options Outstanding at the end of the period (in shares)	6,538,920	7,015,350
Options Vested and Expected to Vest at the end of the period (in shares)	6,506,078
Options Exercisable at the end of the period (in shares)	3,752,500
Shares Available for Grant under the 2008 Plan (in shares)	605,722
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 9.34
Granted (in dollars per share)	$ 25.54
Exercised (in dollars per share)	$ 5.35
Canceled (in dollars per share)	$ 13.11
Options Outstanding at the end of the period (in dollars per share)	$ 9.85	$ 9.34
Options Vested and Expected to Vest at the end of the period (in dollars per share)	$ 9.82
Options Exercisable at the end of the period (in dollars per share)	$ 7.43
Weighted Average Remaining Contractual Term
Options Outstanding at beginning of the period	6 years 8 months 12 days	6 years 7 months 6 days
Options Outstanding at the end of the period	6 years 8 months 12 days	6 years 7 months 6 days
Options Vested and Expected to Vest at the end of the period	6 years 8 months 12 days
Options Exercisable at the end of the period	5 years 3 months 18 days
Additional information
Weighted average grant-date fair value (in dollars per share)	$ 15.94