Accrued Expenses and Other Current Liabilities (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Payables and Accruals [Abstract]    
Payroll and employee benefits $ 49,039 $ 73,362
Taxes other than income taxes 111,362 114,598
Interest 77,375 30,384
Acquired sales contracts 11,635 12,453
Workers’ compensation 15,586 16,714
Asset retirement obligations 19,215 19,222
Other 37,291 35,663
Accrued Liabilities, Current $ 321,503 $ 302,396