Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Other Liabilities Disclosure [Abstract]
Subsidence Liability	$ 87,682	$ 103,343
Accrued Royalties	40,297	52,456
Interest Payable, Current	38,406	51,404
Accrual for Taxes Other than Income Taxes, Current	15,172	17,951
Accrued Bonuses, Current	8,349	49,533
Liability for Uncertain Tax Positions, Current	30,657	37,293
Lease Incentive, Payable, Current	15,286	15,258
Accrued Bonuses	7,714	36,272
Accrued Liabilities and Other Liabilities	78,391	85,026
Other Postretirement Benefits Payable	46,105	57,279
Accrued Reclamation Costs, Current	2,772	9,339
Pneumoconiosis Liability, Current	9,471	9,156
Defined Benefit Pension Plan Liabilities, Current	5,332	6,075
Long Term Disability, Current	4,248	3,957
Mine closing liability, current	14,803	15,122
Gas well closing liability, current	15,648	21,286
Workers' Compensation Liability, Current	30,560	32,222
Other Accrued Liabilities	$ 450,893	$ 602,972