v3.26.1
Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]          
Revenues $ 1,141,014 $ 1,102,361 $ 2,225,292 $ 2,119,767  
Adjusted EBITDA 376,244 204,816 584,703 370,121  
Reconciliation of Segment Profit or Loss Measure to Consolidated Earnings (Loss) Before Income Tax:          
Other Profit or Loss 333 1,244 1,722 1,612  
Depreciation, Depletion and Amortization (166,762) (169,263) (313,057) (290,819)  
General and Administrative Costs (26,669) (34,829) (62,748) (124,152)  
Interest Expense (11,640) (10,051) (22,832) (18,070)  
Interest Income 4,511 6,401 9,259 12,719  
Loss on Debt Extinguishment 0 0 0 (11,680)  
Non-Service Related Pension and Postretirement Benefit Costs (5,659) (6,537) (11,312) (12,739)  
Closed and Idle Mine Costs (4,287) (4,920) (8,767) (9,564)  
Other Operating Income and Expense, net (17,770) (4,948) (7,775) 4,911  
Other Costs (5,331) (11,353) (5,606) (25,272)  
Earnings (Loss) Before Income Tax 142,970 (29,440) 163,587 (102,933)  
Additional Information          
Segment Assets 6,122,353 6,208,738 6,122,353 6,208,738 $ 6,130,053
Depreciation, Depletion and Amortization 166,762 169,263 313,057 290,819  
Capital Expenditures 101,901 89,185 174,998 154,007  
High CV Thermal          
Segment Reporting [Line Items]          
Revenues 612,122 606,500 1,164,954 1,148,586  
Metallurgical          
Segment Reporting [Line Items]          
Revenues 366,283 299,994 708,618 604,574  
PRB          
Segment Reporting [Line Items]          
Revenues 148,274 186,872 323,454 349,461  
Core Marine Terminal          
Segment Reporting [Line Items]          
Revenues 9,942 4,540 18,444 9,496  
Operating Segments          
Segment Reporting [Line Items]          
Revenues 1,153,625 1,115,938 2,248,184 2,146,419  
Operating Segments | High CV Thermal          
Segment Reporting [Line Items]          
Revenues 612,122 606,500 1,164,954 1,148,586  
Cash Costs of Revenue 325,138 331,058 652,963 634,619  
Transportation Costs 122,379 99,084 221,752 192,813  
Other Segment Items 0 0 0 0  
Adjusted EBITDA 164,605 176,358 290,239 321,154  
Reconciliation of Segment Profit or Loss Measure to Consolidated Earnings (Loss) Before Income Tax:          
Depreciation, Depletion and Amortization (61,042) (52,021) (113,718) (103,311)  
Additional Information          
Segment Assets 2,145,462 2,072,304 2,145,462 2,072,304  
Depreciation, Depletion and Amortization 61,042 52,021 113,718 103,311  
Capital Expenditures 63,259 48,175 113,591 82,170  
Operating Segments | Metallurgical          
Segment Reporting [Line Items]          
Revenues 366,283 299,994 708,618 604,574  
Cash Costs of Revenue 223,236 214,365 449,541 425,140  
Transportation Costs 68,808 67,088 136,595 144,070  
Other Segment Items (125,427) 21,243 (135,150) 57,649  
Adjusted EBITDA 199,666 (2,702) 257,632 (22,285)  
Reconciliation of Segment Profit or Loss Measure to Consolidated Earnings (Loss) Before Income Tax:          
Depreciation, Depletion and Amortization (76,256) (75,317) (147,117) (121,206)  
Additional Information          
Segment Assets 1,980,440 2,334,353 1,980,440 2,334,353  
Depreciation, Depletion and Amortization 76,256 75,317 147,117 121,206  
Capital Expenditures 20,467 30,509 34,167 54,473  
Operating Segments | PRB          
Segment Reporting [Line Items]          
Revenues 148,274 186,872 323,454 349,461  
Cash Costs of Revenue 151,678 168,246 314,274 301,404  
Transportation Costs 2,393 2,460 6,100 5,200  
Other Segment Items 0 0 0 0  
Adjusted EBITDA (5,797) 16,166 3,080 42,857  
Reconciliation of Segment Profit or Loss Measure to Consolidated Earnings (Loss) Before Income Tax:          
Depreciation, Depletion and Amortization (8,205) (5,666) (16,505) (16,446)  
Additional Information          
Segment Assets 249,759 361,452 249,759 361,452  
Depreciation, Depletion and Amortization 8,205 5,666 16,505 16,446  
Capital Expenditures 6,081 2,413 6,832 4,909  
Operating Segments | Core Marine Terminal          
Segment Reporting [Line Items]          
Revenues 26,946 22,572 51,158 43,798  
Cash Costs of Revenue 9,176 7,578 17,406 15,403  
Transportation Costs 0 0 0 0  
Other Segment Items 0 0 0 0  
Adjusted EBITDA 17,770 14,994 33,752 28,395  
Reconciliation of Segment Profit or Loss Measure to Consolidated Earnings (Loss) Before Income Tax:          
Depreciation, Depletion and Amortization (1,500) (1,394) (2,979) (2,773)  
Additional Information          
Segment Assets 97,040 87,156 97,040 87,156  
Depreciation, Depletion and Amortization 1,500 1,394 2,979 2,773  
Capital Expenditures 3,404 1,538 5,993 2,780  
Intersegment Revenues          
Segment Reporting [Line Items]          
Revenues (17,004) (18,032) (32,714) (34,302)  
Intersegment Revenues | High CV Thermal          
Segment Reporting [Line Items]          
Revenues 0 0 0 0  
Intersegment Revenues | Metallurgical          
Segment Reporting [Line Items]          
Revenues 0 0 0 0  
Intersegment Revenues | PRB          
Segment Reporting [Line Items]          
Revenues 0 0 0 0  
Intersegment Revenues | Core Marine Terminal          
Segment Reporting [Line Items]          
Revenues (17,004) (18,032) (32,714) (34,302)  
Corporate and Other          
Segment Reporting [Line Items]          
Revenues 4,393 4,455 9,822 7,650  
Reconciliation of Segment Profit or Loss Measure to Consolidated Earnings (Loss) Before Income Tax:          
Depreciation, Depletion and Amortization (19,759) (34,865) (32,738) (47,083)  
Additional Information          
Segment Assets 1,649,652 1,353,473 1,649,652 1,353,473  
Depreciation, Depletion and Amortization 19,759 34,865 32,738 47,083  
Capital Expenditures $ 8,690 $ 6,550 $ 14,415 $ 9,675