Employee Benefits and Share-Based Compensation - Stock Option Activity (Details) (2009 Plan [Member], USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Number of Shares
Outstanding at December 31, 2014	2,672
Granted	151
Exercised	(132)
Expired	0
Forfeited	(16)
Outstanding at March 31, 2015	2,675	2,672
Exercisable at March 31, 2015 (in shares)	1,529
Vested and expected to vest at March 31, 2015 (in shares)	2,643
Weighted Average Exercise Price
Outstanding at December 31, 2014	$ 19.02
Granted	$ 33.73
Exercised	$ 15.69
Expired	$ 0.00
Forfeited	$ 22.60
Outstanding at March 31, 2015	$ 19.98	$ 19.02
Exercisable at March 31, 2015 (in dollars per share)	$ 16.11
Vested and expected to vest at March 31, 2015 (in dollars per share)	$ 19.88
Weighted-average remaining years, outstanding (in years)	6 years 7 months 6 days	6 years 6 months
Weighted-average remaining years, exercisable at December 31, 2014 (in years)	5 years
Weighted-average remaining years, vested and expected to vest at March 31, 2015 (in years)	6 years 6 months
Aggregate Intrinsic Value, outstanding at March 31, 2015	$ 40,442,000
Aggregate Intrinsic Value, exercisable at March 31, 2015	29,042,000
Aggregate Intrinsic Value, vested and expected to vest at March 31, 2015	40,234,000
Employee Stock Option [Member]
Weighted Average Exercise Price
Weighted-average fair value (in usd per share)	$ 9.82	$ 8.29
Intrinsic value of options exercised	2,400,000	5,300,000
Unrecognized compensation cost of unvested stock options	$ 9,200,000
Weighted average period of compensation cost recognized	2 years 9 months