CWP and Workers Comp (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Net Periodic Benefit Cost	$ 22,196	$ 19,053	$ 29,095
Net periodic (benefit) cost	45,463	(198,713)	16,687
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Actuarial Net (Gains) Losses	(23,857)	(119,222)	(46,155)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(392,556)	(359,068)
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	15,897
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	15,193
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	15,061
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	15,044
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	15,056
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	76,577
Workers Compensation [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Curtailments	0	0	0
Defined Benefit Plan, Settlements, Plan Assets	0	347
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Service Cost	7,618	9,389	9,781
Defined Benefit Plan, Interest Cost	2,550	3,195	3,577
Amortization of actuarial gain	(403)	(31)	(382)
State administrative fees and insurance bond premiums	3,265	3,581	3,352
Defined Benefit Plan, Net Periodic Benefit Cost	0	0	0
Legal and administrative costs	7,618	9,389
Net periodic (benefit) cost	13,030	16,134	16,328
Legal and administrative costs	7,618	9,389
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	79,693	83,165	$ 89,741
Defined Benefit Plan, Actuarial Net (Gains) Losses	123	(4,089)
Defined Benefit Plan, Benefits Paid	(17,028)	(18,999)
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	1,458	1,450
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	(67,277)	(69,812)
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(79,693)	(83,165)
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	(13,874)	(14,803)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(12,914)	(13,440)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(12,914)	$ (13,440)
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year [Abstract]
Defined Benefit Plan, Amortization of Net Gains (Losses)	$ (610)
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.26%	3.84%	4.57%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.05%	4.26%	3.84%
Coal Workers Pneumoconiosis [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Curtailments	$ 1,307	$ 0
Defined Benefit Plan, Settlements, Plan Assets	0	0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Service Cost	4,327	6,491	$ 5,674
Defined Benefit Plan, Interest Cost	4,283	5,116	5,537
Amortization of actuarial gain	(4,948)	(5,576)	(6,196)
State administrative fees and insurance bond premiums	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	0	0	0
Legal and administrative costs	4,327	6,491
Net periodic (benefit) cost	2,355	6,031	5,015
Legal and administrative costs	4,327	6,491
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation	118,836	122,503	$ 126,098
Defined Benefit Plan, Actuarial Net (Gains) Losses	439	(5,089)
Defined Benefit Plan, Benefits Paid	(11,409)	(10,113)
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	0	0
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	(108,073)	(113,032)
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(118,836)	(122,503)
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	(10,763)	(9,471)
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(62,714)	(68,101)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax	(62,714)	$ (68,101)
Defined Benefit Plan, Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year [Abstract]
Defined Benefit Plan, Amortization of Net Gains (Losses)	$ (7,631)
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.60%	4.21%	4.75%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.40%	4.60%	4.21%
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	$ 10,763
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	8,417
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	7,606
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	7,137
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	6,963
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	35,714
Deferred Income Taxes and Tax Credits			$ 7,713
Actuarial Benefits [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	12,416
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	11,625
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	11,404
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	11,295
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	11,214
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	55,876
Other Workers Comp benefits [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments in Year One	3,481
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	3,568
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	3,657
Defined Benefit Plan, Expected Future Benefit Payments in Year Four	3,749
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	3,842
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	20,701
Discontinued Operations [Member] | Coal Workers Pneumoconiosis [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Net Periodic Benefit Cost	$ 1,290	$ (297)	$ (87)