Investments - Madison Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 31, 2017	Sep. 24, 2017	Jun. 25, 2017	Mar. 26, 2017	Dec. 25, 2016	Mar. 27, 2016	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 0				$ 1,700						$ 0	$ 1,700
Income Statement Information [Abstract]
Loss from discontinued operations, net of income taxes					57	$ (488)	$ 0	$ 0			0	(431)	$ (2,273)
Income (Loss) from Equity Method Investments	$ 10,773	$ (16)	$ (8)	$ 15	(12,823)	$ 31,557	$ (266)	$ 173			$ 10,764	18,641	(36,273)
Madison Paper Industries Owned Consolidated Subsidiary [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	80.00%										80.00%
Madison Paper Industries
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	40.00%										40.00%
Balance Sheet Information [Abstract]
Current assets	$ 18,374				35,764						$ 18,374	35,764
Noncurrent assets	0				9,640						0	9,640
Total assets	18,374				45,404						18,374	45,404
Current liabilities	3,336				137						3,336	137
Noncurrent liabilities	0				4,070						0	4,070
Total liabilities	3,336				4,207						3,336	4,207
Total equity	$ 15,038				$ 41,197						15,038	41,197
Income Statement Information [Abstract]
Revenues											0	0	40,523
Cost of sales											0	(13,396)	(63,439)
General and administrative income/(expense) and other											(1,280)	55,058	(62,759)
Total income/(expense)											(1,280)	41,662	(126,198)
Operating income/(loss)											(1,280)	41,662	(85,675)
Other income/(expense)											122	18	2
Net income/(loss)											(1,158)	41,680	(85,673)
Income (Loss) from Equity Method Investments											$ 10,800	18,600	$ 36,300
Ownership of Madison Paper Industries by Consolidated Subsidiary [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	50.00%										50.00%
Madison Paper Industries
Schedule of Equity Method Investments [Line Items]
Gain on sale of assets									$ 3,900		$ 11,300	$ 20,800
UPM-Kymmene [Member] | 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 Owned Consolidated Subsidiary [Member]
Income Statement Information [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	20.00%										20.00%
Madison Paper Industries | Madison Paper Industries
Income Statement Information [Abstract]
Noncontrolling Interest, Ownership Percentage by Parent	10.00%										10.00%
Facility Closing [Member] | Madison Paper Industries
Income Statement Information [Abstract]
Income (Loss) from Equity Method Investments										$ 41,400