v3.26.3
Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]          
Revenues $ 1,145,087 $ 1,002,543 $ 3,370,379 $ 3,122,310  
Adjusted EBITDA 218,603 182,384 803,306 552,505  
Reconciliation of Segment Profit or Loss Measure to Consolidated (Loss) Earnings Before Income Tax:          
Other Profit or Loss 3,116 679 4,838 2,291  
Depreciation, Depletion and Amortization (159,302) (151,006) (472,359) (441,825)  
General and Administrative Costs (25,108) (34,133) (87,856) (158,285)  
Interest Expense (10,303) (10,606) (33,135) (28,676)  
Interest Income 5,691 7,578 14,950 20,297  
Loss on Debt Extinguishment 0 0 0 (11,680)  
Non-Service Related Pension and Postretirement Benefit Costs (5,651) (6,562) (16,963) (19,301)  
Closed and Idle Mine Costs (4,048) (5,080) (12,815) (14,644)  
Other Operating Income and Expense, net (6,799) (1,742) (14,574) 3,169  
Other Costs (19,780) (2,912) (25,386) (28,184)  
(Loss) Earnings Before Income Tax (3,581) (21,400) 160,006 (124,333)  
Additional Information          
Segment Assets 6,059,843 6,195,888 6,059,843 6,195,888 $ 6,130,053
Depreciation, Depletion and Amortization 159,302 151,006 472,359 441,825  
Capital Expenditures 94,446 49,297 269,444 203,304  
High CV Thermal          
Segment Reporting [Line Items]          
Revenues 580,969 514,721 1,745,923 1,663,307  
Metallurgical          
Segment Reporting [Line Items]          
Revenues 355,364 292,694 1,063,982 897,268  
PRB          
Segment Reporting [Line Items]          
Revenues 195,143 186,366 518,597 535,827  
Core Marine Terminal          
Segment Reporting [Line Items]          
Revenues 9,200 5,591 27,644 15,087  
Intersegment Terminal Revenues          
Segment Reporting [Line Items]          
Revenues (15,490) (14,187) (48,204) (48,488)  
Intersegment Terminal Revenues | High CV Thermal          
Segment Reporting [Line Items]          
Revenues 0 0 0 0  
Intersegment Terminal Revenues | Metallurgical          
Segment Reporting [Line Items]          
Revenues 0 0 0 0  
Intersegment Terminal Revenues | PRB          
Segment Reporting [Line Items]          
Revenues 0 0 0 0  
Intersegment Terminal Revenues | Core Marine Terminal          
Segment Reporting [Line Items]          
Revenues (15,490) (14,187) (48,204) (48,488)  
Operating Segments          
Segment Reporting [Line Items]          
Revenues 1,156,166 1,013,559 3,404,350 3,159,977  
Operating Segments | High CV Thermal          
Segment Reporting [Line Items]          
Revenues 580,969 514,721 1,745,923 1,663,307  
Cash Costs of Revenue 341,106 293,002 994,069 927,621  
Transportation Costs 115,240 82,550 336,992 275,363  
Other Segment Items   0 0 0  
Adjusted EBITDA 124,623 139,169 414,862 460,323  
Reconciliation of Segment Profit or Loss Measure to Consolidated (Loss) Earnings Before Income Tax:          
Depreciation, Depletion and Amortization (66,829) (52,842) (180,547) (156,153)  
Additional Information          
Segment Assets 1,952,642 2,179,909 1,952,642 2,179,909  
Depreciation, Depletion and Amortization 66,829 52,842 180,547 156,153  
Capital Expenditures 57,242 40,642 170,833 122,812  
Operating Segments | Metallurgical          
Segment Reporting [Line Items]          
Revenues 355,364 292,694 1,063,982 897,268  
Cash Costs of Revenue 227,669 209,285 677,210 634,425  
Transportation Costs 60,911 66,912 197,506 210,982  
Other Segment Items   (975) (135,150) 56,674  
Adjusted EBITDA 66,784 17,472 324,416 (4,813)  
Reconciliation of Segment Profit or Loss Measure to Consolidated (Loss) Earnings Before Income Tax:          
Depreciation, Depletion and Amortization (69,914) (65,381) (217,031) (186,587)  
Additional Information          
Segment Assets 1,918,288 2,140,661 1,918,288 2,140,661  
Depreciation, Depletion and Amortization 69,914 65,381 217,031 186,587  
Capital Expenditures 17,051 2,719 51,218 57,192  
Operating Segments | PRB          
Segment Reporting [Line Items]          
Revenues 195,143 186,366 518,597 535,827  
Cash Costs of Revenue 181,541 169,945 495,815 471,349  
Transportation Costs 2,944 2,830 9,044 8,030  
Other Segment Items   0 0 0  
Adjusted EBITDA 10,658 13,591 13,738 56,448  
Reconciliation of Segment Profit or Loss Measure to Consolidated (Loss) Earnings Before Income Tax:          
Depreciation, Depletion and Amortization (8,484) (8,795) (24,989) (25,241)  
Additional Information          
Segment Assets 250,185 422,024 250,185 422,024  
Depreciation, Depletion and Amortization 8,484 8,795 24,989 25,241  
Capital Expenditures 8,581 1,876 15,413 6,785  
Operating Segments | Core Marine Terminal          
Segment Reporting [Line Items]          
Revenues 24,690 19,778 75,848 63,575  
Cash Costs of Revenue 8,152 7,626 25,558 23,028  
Transportation Costs 0 0 0 0  
Other Segment Items   0 0 0  
Adjusted EBITDA 16,538 12,152 50,290 40,547  
Reconciliation of Segment Profit or Loss Measure to Consolidated (Loss) Earnings Before Income Tax:          
Depreciation, Depletion and Amortization (1,591) (1,398) (4,570) (4,171)  
Additional Information          
Segment Assets 95,592 92,521 95,592 92,521  
Depreciation, Depletion and Amortization 1,591 1,398 4,570 4,171  
Capital Expenditures 4,441 3,104 10,434 5,884  
Corporate and Other          
Segment Reporting [Line Items]          
Revenues 4,411 3,171 14,233 10,821  
Reconciliation of Segment Profit or Loss Measure to Consolidated (Loss) Earnings Before Income Tax:          
Depreciation, Depletion and Amortization (12,484) (22,590) (45,222) (69,673)  
Additional Information          
Segment Assets 1,843,136 1,360,773 1,843,136 1,360,773  
Depreciation, Depletion and Amortization 12,484 22,590 45,222 69,673  
Capital Expenditures $ 7,131 $ 956 $ 21,546 $ 10,631