v3.26.1
Segments - Significant Operating Expenses (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 27, 2026
Jun. 28, 2025
Sep. 28, 2024
Jun. 27, 2026
Jun. 28, 2025
Segment Reporting [Line Items]          
Total consolidated net sales $ 376,142 $ 340,048   $ 695,207 $ 696,015
Total segment cost of sales 353,197 316,407   679,855 648,320
Selling, general and administrative expense 17,238 17,965   36,409 41,224
Temiscaming HPC permanent idling charges 0 0   40,883 0
Asset impairment 13,037 0   13,037 0
Suspension charges 827 229   955 634
Operating loss (6,343) (1,339)   (71,658) (16,432)
Interest expense (24,714) (23,694)   (47,828) (47,297)
Components of pension and OPEB, excluding service costs 1,122 673   2,155 1,305
Other expense, net (137) (1,800)   (1,089) (908)
Loss from continuing operations before income tax (30,072) (26,160)   (118,420) (63,332)
Other segment items          
Depreciation and amortization       65,450 62,438
Temiscaming HPC permanent idling charges - accelerated depreciation       34,494 0
Total consolidated depreciation and amortization 31,997 31,187   99,944 62,438
High Purity Cellulose          
Segment Reporting [Line Items]          
Asset impairment     $ 25,000    
Operating Segments          
Segment Reporting [Line Items]          
Total consolidated net sales 376,126 339,979   695,120 695,886
Total segment cost of sales 353,477 316,585   680,030 648,250
Operating loss 2,168 12,413   (51,214) 23,913
Other segment items          
Depreciation and amortization 31,001 30,658   63,048 61,568
Temiscaming HPC permanent idling charges - accelerated depreciation       34,494 0
Total consolidated depreciation and amortization       97,542 61,568
Operating Segments | High Purity Cellulose          
Segment Reporting [Line Items]          
Total consolidated net sales 301,462 271,960   564,363 553,982
Key input costs (wood, chemicals, energy) 228,436 109,219   226,673 227,727
Fixed and other costs of sales 38,474 135,300   302,500 269,738
Total segment cost of sales 266,910 244,519   529,173 497,465
Selling, general and administrative expense 6,756 6,009   12,827 13,770
Temiscaming HPC permanent idling charges       40,883 0
Asset impairment 0 0   0 0
Suspension charges 827 229   955 634
Other segment items (2,322) 1,380   (5,583) 1,995
Operating loss 29,291 19,823   (13,892) 40,118
Other segment items          
Depreciation and amortization 27,395 24,730   55,495 49,813
Temiscaming HPC permanent idling charges - accelerated depreciation       34,494 0
Total consolidated depreciation and amortization       89,989 49,813
Operating Segments | Paperboard & High Yield Pulp          
Segment Reporting [Line Items]          
Total consolidated net sales 74,664 68,019   130,757 141,904
Key input costs (wood, chemicals, energy) 31,061 32,539   61,985 71,564
Fixed and other costs of sales 55,506 39,527   88,872 79,221
Total segment cost of sales 86,567 72,066   150,857 150,785
Selling, general and administrative expense 2,183 3,354   4,167 6,844
Temiscaming HPC permanent idling charges       0 0
Asset impairment 13,037 0   13,037 0
Suspension charges 0 0   0 0
Other segment items 0 9   18 480
Operating loss (27,123) (7,410)   (37,322) (16,205)
Other segment items          
Depreciation and amortization 3,606 5,928   7,553 11,755
Temiscaming HPC permanent idling charges - accelerated depreciation       0 0
Total consolidated depreciation and amortization       7,553 11,755
Operating Segments | Cellulose Specialties          
Segment Reporting [Line Items]          
Total consolidated net sales 188,508 200,126   336,580 394,678
Corporate & Other          
Segment Reporting [Line Items]          
Total consolidated net sales 16 69   87 129
Operating loss (8,511) (13,752)   (20,444) (40,345)
Other segment items          
Total consolidated depreciation and amortization $ 996 $ 529   $ 2,402 $ 870