Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Payroll and employee benefits	$ 50,429	$ 73,362
Taxes other than income taxes	110,666	114,598
Interest	30,452	30,384
Acquired sales contracts	6,167	12,453
Workers’ compensation	17,220	16,714
Asset retirement obligations	19,210	19,222
Other	28,814	35,663
Accrued Liabilities, Current	$ 262,958	$ 302,396