Revenue Recognition (Tables)

3 Months Ended

Mar. 31, 2018

Revenue from Contract with Customer [Abstract]

Schedule of effects of revenue recognition

	PRB		MET		Other Thermal		Corporate, Other and Eliminations		Consolidated
	(in thousands)
Three Months Ended March 31, 2018
North America revenues	$	244,360	$	29,678	$	43,667	$	—	$	317,705
Seaborne revenues	1,068		208,669		47,853		—		257,590
Total revenues	$	245,428	$	238,347	$	91,520	$	—	$	575,295
Three Months Ended March 31, 2017
North America revenues	$	273,428	$	68,734	$	68,964	$	59	$	411,185
Seaborne revenues	—		156,848		32,942		—		189,790
Total revenues	$	273,428	$	225,582	$	101,906	$	59	$	600,975