Share-Based Compensation - Summary of Activity for Stock Options Granted (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning of Period, (in shares)	2,726,553	1,955,799	1,283,116
Beginning of Period, Weighted Average Exercise Price (in usd per share)	$ 23.51	$ 17.92	$ 16.34
Beginning of Period, Weighted Average Remaining Contractual Term (in years)	6 years 4 months 1 day	7 years 2 months 19 days	7 years 7 days	8 years 6 months 4 days
Beginning of Period	$ 32,785	$ 49,458	$ 6,042
Granted (in shares)	67,507	1,050,904	800,820
Granted (in usd per share)	$ 29.11	$ 33.79	$ 20.56
Exercised (in shares)	(303,449)	(166,711)	(87,598)
Exercised (in usd per share)	$ 18.12	$ 17.39	$ 14.13
Exercised	3,468	3,561	1,410
Forfeited or expired (in shares)	(126,883)	(113,439)	(40,539)
Forfeited or expired (in usd per share)	$ 31.24	$ 31.33	$ 28.33
End of Period, (in shares)	2,363,728	2,726,553	1,955,799	1,283,116
End of Period, Weighted Average Exercise Price (in usd per share)	$ 23.95	$ 23.51	$ 17.92	$ 16.34
End of Period, Weighted Average Remaining Contractual Term (in years)	6 years 4 months 1 day	7 years 2 months 19 days	7 years 7 days	8 years 6 months 4 days
End of Period	1,223	32,785	49,458	6,042
End of Period, Exercisable (in shares)	1,236,543
End of Period, Exercisable (in usd per share)	$ 17.40
End of Period, Exercisable (in years)	5 years 2 months 18 days
End of Period, Exercisable	1,223
Options expected to vest as of December 31, 2014 (in shares)	1,110,672
Options expected to vest as of December 31, 2014 (in usd per shares)	$ 31.09
Options expected to vest as of December 31, 2014 (in years)	7 years 6 months 21 days
Options expected to vest as of December 31, 2014	$ 0