Share-Based Compensation - Summary of Activity for Non-Vested Awards 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, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance ( in shares)	308,426	815,928	1,766,960
Beginning Balance (in usd per share)	$ 25.65	$ 22.32	$ 15.84
Beginning Balance (in years)	1 year 10 months 1 day	1 year 10 months 24 days	3 years 1 month 2 days	5 years 7 months 24 days
Beginning Balance	$ 10,906	$ 35,101	$ 36,240
Granted (in shares)	738,164	36,576	110,783
Granted (in dollars per share)	$ 32.46	$ 35.79	$ 20.72
Vested and Settled (in shares)	(30,898)	(522,762)	(969,815)
Vested and settled	910	20,922	20,189
Vested and settled (in usd per share)	$ 29.45
Forfeited (in shares)	(94,133)	(21,316)	(92,000)
Forfeited (in usd per share)	$ 8.48	$ 25.73	$ 24.93
Ending Balance ( in shares)	921,559	308,426	815,928	1,766,960
Ending Balance (in usd per share)	$ 30.42	$ 25.65	$ 22.32	$ 15.84
Ending Balance (in years)	1 year 10 months 1 day	1 year 10 months 24 days	3 years 1 month 2 days	5 years 7 months 24 days
Ending Balance	15,215	10,906	35,101	36,240
Non-vested shares expected to vest as of December 31, 2014 (in shares)	901,631
Non-vested shares expected to vest as of December 31, 2014 (in usd per share)	$ 30.39
Non-vested shares expected to vest as of December 31, 2014 (in years)	1 year 10 months 0 days
Non-vested shares expected to vest as of December 31, 2014	$ 14,886