Taxes (Schedule of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 1,086,332	$ 871,848
Alternative minimum tax credit carryforwards	120,994	127,169
Reclamation and mine closure	121,276	114,430
Goodwill	38,671	50,072
Workers' compensation	42,835	38,924
Share based compensation	22,612	30,283
Acquired sales contracts	17,466	26,833
Retiree benefit plans	16,996	22,913
Contract obligations	0	15,693
Advance royalties	18,751	0
Losses from disposed operations resulting from Patriot Coal bankruptcy	39,287	0
Other, primarily accrued liabilities	45,303	64,503
Gross deferred tax assets	1,570,523	1,362,668
Valuation allowance	(1,135,399)	(270,251)
Total deferred tax assets	435,124	1,092,417
Plant and equipment	389,169	1,354,396
Deferred development	41,047	95,129
Investment in tax partnerships	0	7,377
Other	4,706	5,533
Total deferred tax liabilities	434,922	1,462,435
Net deferred (asset) liability		$ 370,018
Net deferred (asset) liability	$ (202)