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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Number of Shares
Outstanding at December 31, 2013	3,143
Granted	641
Exercised	(1,007)
Expired	(12)
Forfeited	(93)
Outstanding at December 31, 2014	2,672	3,143
Exercisable at December 31, 2014	1,514
Vested and expected to vest at December 31, 2014	2,640
Weighted Average Exercise Price
Outstanding at December 31, 2013	$ 15.82
Granted	$ 28.11
Exercised	$ 14.74
Expired	$ 19.88
Forfeited	$ 19.97
Outstanding at December 31, 2014	$ 19.02	$ 15.82
Exercisable at December 31, 2014	$ 15.66
Vested and expected to vest at December 31, 2014	$ 18.92
Outstanding at December 31 (in years)	6 years 6 months	5 years 7 months 6 days
Exercisable at December 31, 2014 (in years)	4 years 8 months 12 days
Vested and expected to vest at December 31, 2014 (in years)	6 years 4 months 24 days
Outstanding at December 31, 2014	$ 37,692,000
Exercisable at December 31, 2014	26,447,000
Vested and expected to vest at December 31, 2014	37,481,000
Employee Stock Option [Member]
Weighted Average Exercise Price
Weighted-average fair value (in usd per share)	$ 9.12	$ 8.09	$ 6.13
Intrinsic value of options exercised	14,100,000	14,000,000	2,800,000
Unrecognized compensation cost of unvested stock options	$ 8,800,000
Weighted average period of compensation cost recognized	2 years 9 months 18 days