Stock-Based Compensation (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Additional disclosures
Stock based compensation expense	$ 21,500,000		$ 51,800,000		$ 33,500,000
Stock Appreciation Rights
Stock-Based Compensation arrangements
Graded vesting rights	3 years
Vesting rights	one-third of the award becoming exercisable each year on the anniversary date of the grant
Contractual term	7 years
Summary of Stock Appreciation Rights Activity (in shares)
Outstanding at beginning of period	667,764	[1]	1,722,444	[1]	2,576,260
Granted			0		240,884
Exercised	0		(1,054,680)		(1,094,700)
Outstanding at end of period(1)	667,764	[1]	667,764	[1]	1,722,444	[1]
Exercisable at end of period(2)	590,960	[2]	386,582	[2]	1,145,972	[2]
Weighted-Average Exercise Price (in dollars per share)
Outstanding at beginning of period	$ 12.63	[1]	$ 9.75	[1]	$ 8.02
Granted			$ 0.00		$ 17.59
Exercised	$ 0.00		$ 7.92		$ 7.42
Outstanding at end of period(1)	$ 12.63	[1]	$ 12.63	[1]	$ 9.75	[1]
Exercisable at end of period(2)	$ 11.98	[2]	$ 11.33	[2]	$ 7.97	[2]
Additional disclosures
Aggregate intrinsic value of stock appreciation rights outstanding	11,300,000
Weighted-average remaining contractual term of non-vested shares	3 years 3 months 18 days
Aggregate intrinsic value of stock appreciation rights exercisable	10,400,000
Stock appreciation rights exercisable, weighted average remaining contractual term	3 years 2 months 12 days
Stock based compensation expense	100,000		300,000		1,900,000
Compensation expenses related to the immediate expensing of shares granted to retirement-eligible employees					1,200,000
Unamortized compensation expense	$ 0
Weighted-average value per SAR granted during the period (in dollars per share)					$ 8.16
Assumptions
Stock price volatility					55.30%
Risk free rate of return					0.90%
Expected dividend yield (as a percent)					0.30%
Expected term					5 years

[1] The intrinsic value of a SAR is the amount which the current market value of the underlying stock exceeds the exercise price of the SAR. As of December 31, 2014, the aggregate intrinsic value and weighted-average remaining contractual term of SARs outstanding was $11.3 million and 3.3 years, respectively.

[2] As of December 31, 2014, the aggregate intrinsic value and weighted-average remaining contractual term of SARs exercisable was $10.4 million and 3.2 years, respectively.