Stockholder's Equity and Stock Based Compensation (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Stockholder's Equity and Stock Based Compensation
Common stock, shares authorized	1,000,000,000
Common stock, par value (in dollars per share)	$ 0.0001
Preferred stock, shares authorized	20,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001
Common stock, shares issued	42,100,000
Common stock, shares outstanding	42,100,000
Stock options to purchase common stock
Number of Stock Options Outstanding
Balance at the beginning of the period (in shares)	5,404,000
Exercised (in shares)	(278,000)
Cancelled/Forfeited (in shares)	(157,000)
Balance at the end of the period (in shares)	4,969,000		5,404,000
Exercisable at the end of the period (in shares)	4,163,000
Vested and expected to vest at the end of the period (in shares)	4,682,000
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 11.55
Exercised (in dollars per share)	$ 3.47
Cancelled/Forfeited (in dollars per share)	$ 12.79
Balance at end of the period (in dollars per share)	$ 11.96		$ 11.55
Exercisable at the end of the period (in dollars per share)	$ 7.27
Vested and expected to vest at the end of the period (in dollars per share)	$ 11.50
Weighted-Average Remaining Contractual Life
Outstanding at the beginning of the period	7 years 2 months 5 days		7 years 6 months 22 days
Outstanding at the end of the period	7 years 2 months 5 days		7 years 6 months 22 days
Exercisable at the end of the period	7 years 4 days
Vested and expected to vest at the end of the period	7 years 1 month 17 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period	$ 120,595,000
Outstanding at the end of the period	80,350,000		120,595,000
Exercisable at the end of the period	79,948,000
Vested and expected to vest at the end of the period	77,198,000
Closing stock price (in dollars per share)	$ 25.62
Additional information
Weighted average grant date fair value (in dollars per share)		$ 21.78
Total intrinsic value of options exercised	7,583,000	28,623,000
Total estimated grant date fair value of options vested	$ 5,700,000
Stock options to purchase common stock | 2006 Stock Plan
Additional information
Vesting period	4 years
Percentage of awards which will vest after one year	25.00%