Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 450,389	$ 319,521	$ 807,932	$ 724,753
Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	182	6,177	1,404	18,559
North America revenues
Disaggregation of Revenue [Line Items]
Revenues	247,711	210,559	437,981	459,527
North America revenues | Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	182	6,177	1,404	18,559
Seaborne revenues
Disaggregation of Revenue [Line Items]
Revenues	202,678	108,962	369,951	265,226
Seaborne revenues | Corporate, Other and Eliminations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
MET | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	219,448	138,951	398,231	321,605
MET | North America revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	47,290	40,137	72,127	69,860
MET | Seaborne revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	172,158	98,814	326,104	251,745
Thermal | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	230,759	174,393	408,297	384,589
Thermal | North America revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	200,239	164,245	364,450	371,108
Thermal | Seaborne revenues | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues	$ 30,520	$ 10,148	$ 43,847	$ 13,481