Segment Information (Schedule Of Operating Segment Results) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 688,544	$ 742,180	$ 2,010,011	$ 2,191,927
Adjusted EBITDA	134,805	71,902	261,905	164,439
Depreciation, depletion and amortization	103,965	105,155	306,211	312,042
Amortization of acquired sales contracts, net	(1,994)	(3,013)	(7,028)	(9,948)
Total assets	5,847,997		5,847,997		$ 8,429,723
Capital expenditures	9,889	22,955	109,250	118,701
Operating Segments [Member] | PRB [Member]
Segment Reporting Information [Line Items]
Revenues	390,360	389,386	1,124,046	1,106,258
Adjusted EBITDA	86,204	62,771	214,920	135,136
Depreciation, depletion and amortization	47,321	43,962	134,393	124,243
Amortization of acquired sales contracts, net	(1,124)	(1,200)	(3,170)	(2,774)
Total assets	1,711,945		1,711,945
Capital expenditures	869	8,174	22,263	17,230
Operating Segments [Member] | APP [Member]
Segment Reporting Information [Line Items]
Revenues	205,573	272,354	653,310	832,452
Adjusted EBITDA	41,754	12,327	92,988	67,794
Depreciation, depletion and amortization	44,098	48,867	135,028	155,087
Amortization of acquired sales contracts, net	(870)	(1,815)	(3,858)	(7,266)
Total assets	1,374,436		1,374,436
Capital expenditures	3,990	9,240	15,323	28,232
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	92,611	80,440	232,655	251,239
Adjusted EBITDA	12,927	22,412	22,074	44,007
Depreciation, depletion and amortization	11,193	10,499	32,082	29,601
Amortization of acquired sales contracts, net	0	3	0	93
Total assets	321,449		321,449
Capital expenditures	2,889	4,678	7,199	8,626
Intersegment Eliminations [Member] | Corporate, Other and Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	1,978
Adjusted EBITDA	(6,080)	(25,608)	(68,077)	(82,498)
Depreciation, depletion and amortization	1,353	1,827	4,708	3,111
Amortization of acquired sales contracts, net	0	(1)	0	(1)
Total assets	2,440,167		2,440,167
Capital expenditures	$ 2,141	$ 863	$ 64,465	$ 64,613