Segment Information (Schedule of Operating Segment Results) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 719,386	$ 791,269	$ 766,332	$ 737,370	$ 867,034	$ 975,170	$ 965,685	$ 960,237	$ 3,014,357	$ 3,768,126	$ 3,883,039
Income (loss) from operations		(234,753)	(36,279)	(51,431)	(307,158)	119,242	(596,893)	27,797	(663,141)	(757,012)	343,061
Depreciation, depletion and amortization									426,442	492,211	420,980
Depreciation, depletion and amortization									447,704	525,508	466,587
Amortization of acquired sales contracts, net									(9,457)	(25,189)	(22,069)
Sales contract amortization									(9,457)	(25,189)	(22,069)
Total assets	8,990,193				10,006,777				8,990,193	10,006,777	10,213,959
Capital expenditures									296,984	395,225	540,936
PRB [Member]
Segment Reporting Information [Line Items]
Revenues									1,482,813	1,524,536	1,646,947
Income (loss) from operations									41,543	100,679	180,730
Depreciation, depletion and amortization									171,324	166,539
Depreciation, depletion and amortization											171,693
Sales contract amortization									(3,656)	(1,987)	19,458
Total assets	1,841,835								1,841,835		2,307,783
Capital expenditures									9,784	23,410	110,999
APP [Member]
Segment Reporting Information [Line Items]
Revenues									1,145,800	1,793,576	1,915,090
Income (loss) from operations									(108,387)	(606,235)	283,404
Depreciation, depletion and amortization									202,952	271,220
Depreciation, depletion and amortization											203,759
Sales contract amortization									(10,364)	(23,926)	(39,988)
Total assets	3,971,764								3,971,764		4,740,723
Capital expenditures									167,759	275,476	217,435
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues									385,744	450,014	321,002
Income (loss) from operations									64,943	74,142	44,465
Depreciation, depletion and amortization									45,741	49,911
Depreciation, depletion and amortization											43,504
Sales contract amortization									4,563	724	(1,539)
Total assets	402,922				834,287				402,922	834,287	1,262,433
Capital expenditures									23,122	68,220	94,599
Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues
Income (loss) from operations									(661,240)	(325,598)	(165,538)
Depreciation, depletion and amortization									6,425	4,541
Depreciation, depletion and amortization											2,024
Sales contract amortization
Total assets	2,773,672				3,324,863				2,773,672	3,324,863	1,903,020
Capital expenditures									$ 96,319	$ 28,119	$ 117,903