Segment Information (Schedule of Industry Segment Results) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									$ 1,375,559	$ 1,472,790	$ 1,321,412
Earnings (Loss) Before Income Tax	$ 22,183	$ 9,439	$ 47,022	$ 19,453	$ 46,335	$ 8,394	$ 55,741	$ 77,143	98,097	187,613	169,797
Segment Assets	2,693,802				2,760,727				2,693,802	2,760,727	2,707,099
Depreciation, Depletion and Amortization	55,852	54,370	46,151	50,724	45,590	51,242	54,961	49,471	207,097	201,264	172,002
Capital Expenditures									169,739	145,749	81,413
PAMC
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									1,308,196	1,407,864	1,261,346
Earnings (Loss) Before Income Tax									197,112	291,418	189,162
Segment Assets	1,981,721				1,894,209				1,981,721	1,894,209	1,971,268
Depreciation, Depletion and Amortization									185,616	178,969	166,628
Capital Expenditures									148,709	124,570	77,981
Other
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									67,363	64,926	60,066
Earnings (Loss) Before Income Tax									(99,015)	(103,805)	(19,365)
Segment Assets	712,081				866,518				712,081	866,518	735,831
Depreciation, Depletion and Amortization									21,481	22,295	5,374
Capital Expenditures									21,030	21,179	3,432
Coal Revenue
Segment Reporting Information [Line Items]
Revenue from Contract with Customers	303,865	301,542	350,620	332,502	347,789	294,797	370,697	351,009	1,288,529	1,364,292	1,187,654
Coal Revenue | PAMC
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									1,288,529	1,364,292	1,187,654
Coal Revenue | Other
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									0	0	0
Terminal Revenue
Segment Reporting Information [Line Items]
Revenue from Contract with Customers	16,534	16,303	16,708	17,818	16,931	16,115	16,659	15,221	67,363	64,926	60,066
Terminal Revenue | PAMC
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									0	0	0
Terminal Revenue | Other
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									67,363	64,926	60,066
Freight Revenue
Segment Reporting Information [Line Items]
Revenue from Contract with Customers	$ 5,552	$ 3,599	$ 3,854	$ 6,662	$ 5,798	$ 2,443	$ 17,444	$ 17,887	19,667	43,572	73,692
Freight Revenue | PAMC
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									19,667	43,572	73,692
Freight Revenue | Other
Segment Reporting Information [Line Items]
Revenue from Contract with Customers									$ 0	$ 0	$ 0