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Investments - Equity Method Investments (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Sep. 24, 2017
Dec. 25, 2016
Sep. 30, 2018
Sep. 24, 2017
Dec. 31, 2017
Dec. 25, 2016
Schedule of Equity Method Investments [Line Items]              
Investments in joint ventures $ 1,700,000     $ 1,700,000      
Loss from joint ventures 16,000 $ (31,557,000)   9,000 $ (31,464,000)    
Loss from discontinued operations, net of income taxes $ 0 488,000   $ 0 488,000    
Madison Paper Industries              
Schedule of Equity Method Investments [Line Items]              
Equity method investment, ownership percentage 40.00%     40.00%      
Loss from joint ventures           $ (20,800,000) $ 41,400,000
Investment in Madison     $ 0       $ 0
Gain on sale of non-hydro power assets     $ 3,900,000        
Distributions received $ 0 $ 0   $ 0 $ 0    
Madison Paper Industries Owned Consolidated Subsidiary              
Schedule of Equity Method Investments [Line Items]              
Equity method investment, ownership percentage 80.00%     80.00%      
Ownership of Madison Paper Industries by Consolidated Subsidiary              
Schedule of Equity Method Investments [Line Items]              
Equity method investment, ownership percentage 50.00%     50.00%      
UPM-Kymmene | Madison Paper Industries              
Schedule of Equity Method Investments [Line Items]              
Equity method investment, ownership percentage 60.00%     60.00%      
Madison Paper Industries | Madison Paper Industries              
Schedule of Equity Method Investments [Line Items]              
Noncontrolling interest, ownership percentage by parent 10.00%     10.00%      
Madison Paper Industries | Madison Paper Industries Owned Consolidated Subsidiary              
Schedule of Equity Method Investments [Line Items]              
Noncontrolling interest, ownership percentage by parent 20.00%     20.00%