Accrued Expenses and Other Current Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accrued Expenses and Other Current Liabilities [Abstract]
Payroll and employee benefits	$ 62,486	$ 67,621
Taxes other than income taxes	116,176	114,664
Interest	32,765	18,528
Acquired sales contracts	13,468	14,373
Workers’ compensation	17,783	12,434
Asset retirement obligations	22,682	24,940
Other	28,957	26,027
Accrued Liabilities, Current	$ 294,317	$ 278,587