Summary of Significant Accounting Policies (Details 5) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Stock-based compensation costs
Time period of historical volatility of stock used to estimate expected volatility			5 years 5 months 12 days
Expected dividend yield assumption (as a percent)			0.00%
Granted (in shares)			1,689,357
Accrued salaries and wages	$ 86,069		$ 86,069		$ 84,034
Stock based compensation expense	2,300	$ 2,500	$ 4,400	$ 5,100
Weighted-average assumptions used in the Black-Scholes option-pricing model
Risk-free interest rate (as a percent)			1.75%	1.68%
Expected volatility (as a percent)			32.52%	44.80%
Weighted-average expected life (years)			5 years 5 months 12 days	5 years 5 months 12 days
Phantom Share Units (PSUs)
Stock-based compensation costs
Accrued salaries and wages	11,900		$ 11,900		8,200
Total compensation cost related to nonvested awards not yet recognized	25,200		$ 25,200
Period for recognition of unrecognized compensation cost			2 years 1 month 6 days
Stock based compensation expense	5,000	1,200	$ 9,500	$ 2,600
Amounts paid on cash settled awards	100	100	$ 5,300	6,000
Phantom Share Units (PSUs) | Minimum
Stock-based compensation costs
Vesting period			3 years
Phantom Share Units (PSUs) | Maximum
Stock-based compensation costs
Vesting period			5 years
Stock Appreciation Rights (SARs)
Stock-based compensation costs
Vesting period			4 years
Accrued salaries and wages	11,100		$ 11,100		$ 6,300
Total compensation cost related to nonvested awards not yet recognized	10,200		$ 10,200
Period for recognition of unrecognized compensation cost			2 years 10 months 2 days
Stock based compensation expense	2,500		$ 7,100	100
Stock based compensation, net		(200)
Amounts paid on cash settled awards	$ 500	$ 700	$ 2,300	$ 1,200