Stock-Based Compensation - Summary of the Company's PRSU Activity (Details) (PRSUs, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
PRSUs
Summary of the Company's RSU activity
Outstanding at the beginning of the period	500,000	500,000	700,000
Granted	100,000	200,000	100,000
Additional performance shares	100,000	300,000	200,000
Issued	(300,000)	(500,000)	(500,000)
Outstanding at the end of the period	443,969	500,000	500,000
Weighted-Average Grant Date Fair Value
Outstanding at the beginning of the period	$ 24.60	$ 16.93	$ 11.53
Granted	$ 43.01	$ 28.27	$ 25.03
Additional performance shares	$ 19.02	$ 10.72	$ 8.00
Issued	$ 19.01	$ 10.64	$ 8.28
Outstanding at the end of the period	$ 31.68	$ 24.60	$ 16.93