Stock-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Stock-Based Compensation arrangements
Stock based compensation expense	$ 21,500,000		$ 51,800,000		$ 33,500,000
Tax benefits realized for stock-based compensation	(1,400,000)		18,900,000		0
Restricted Stock Awards
Stock-Based Compensation arrangements
Stock based compensation expense	1,000,000		200,000		1,100,000
Summary of restricted stock award activity (in shares)
Outstanding at beginning of period	27,806	[1],[2]	71,508	[1],[2]	476,388
Granted	47,500		7,200		13,100
Vested	(17,437)		(50,902)		(402,800)
Forfeited	(8,000)		0		(15,180)
Outstanding at end of period	49,869	[1],[2]	27,806	[1],[2]	71,508	[1],[2]
Weighted-Average Grant Date Fair Value per Share (in usd per share)
Outstanding at beginning of period	$ 20.53	[1],[2]	$ 11.82	[1],[2]	$ 9.18
Granted	$ 34.76		$ 35.70		$ 18.42
Vested	$ 15.84		$ 10.44		$ 9.03
Forfeited	$ 35.00		$ 0.00		$ 8.80
Outstanding at end of period	$ 33.40	[1],[2]	$ 20.53	[1],[2]	$ 11.82	[1],[2]
Additional disclosures
Aggregate intrinsic value	1,500,000
Weighted-average remaining contractual term of non-vested shares	1 year 10 months 24 days
Unamortized compensation expense	800,000
Total fair value of shares vested	$ 600,000		$ 1,600,000		$ 3,600,000
Restricted Stock Awards | Greater than
Stock-Based Compensation arrangements
Annual forfeiture rate assumption (as a percent)	5.00%
Restricted Stock Awards | Less than or equal to
Stock-Based Compensation arrangements
Annual forfeiture rate assumption (as a percent)	7.00%
Restricted Stock - 3 Year Service Awards
Stock-Based Compensation arrangements
Vesting period	3 years
Restricted Stock - Graded Vesting | Greater than
Stock-Based Compensation arrangements
Vesting period	3 years
Restricted Stock - Graded Vesting | Less than or equal to
Stock-Based Compensation arrangements
Vesting period	4 years

[1] As of December 31, 2014, the weighted average remaining contractual term of non-vested restricted stock awards outstanding was 1.9 years.

[2] As of December 31, 2014, the aggregate intrinsic value was $1.5 million and was calculated by multiplying the closing market price of the Company's stock on December 31, 2014 by the number of non-vested restricted stock awards outstanding.