Segment reporting - Financial Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 29, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total Revenue
Total Revenue									$ 5,522,703	$ 5,531,203	$ 5,188,107
Net sales	$ 1,308,850	$ 1,353,931	$ 1,359,721	$ 1,351,705	$ 1,355,616	$ 1,364,762	$ 1,366,373	$ 1,304,187	5,374,207	5,390,938	5,036,650
Income Before Income Taxes
Income Before Income Taxes									380,766	378,531	314,554
Identifiable Assets
Identifiable Assets	5,126,289				4,583,465				5,126,289	4,583,465	4,557,721
Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization									239,140	236,245	217,625
Capital Expenditures
Capital Expenditures									195,934	192,574	188,913
Consumer Packaging
Total Revenue
Net sales									2,333,386	2,359,999
Display and Packaging
Total Revenue
Net sales									554,125	592,309
Operating segments | Consumer Packaging
Total Revenue
Total Revenue									2,338,881	2,363,292	2,129,022
Net sales									2,333,386	2,359,999	2,123,465
Income Before Income Taxes
Income Before Income Taxes									228,416	224,505	255,759
Identifiable Assets
Identifiable Assets	2,239,674				1,993,417				2,239,674	1,993,417	1,890,516
Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization									111,919	116,841	98,882
Capital Expenditures
Capital Expenditures									64,590	66,659	63,617
Operating segments | Display and Packaging
Total Revenue
Total Revenue									558,747	595,855	511,099
Net sales									554,125	592,309	508,236
Income Before Income Taxes
Income Before Income Taxes									27,723	13,291	2,632
Identifiable Assets
Identifiable Assets	452,155				440,972				452,155	440,972	480,892
Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization									14,926	18,020	17,090
Capital Expenditures
Capital Expenditures									5,065	19,849	23,908
Operating segments | Paper and Industrial Converted Products
Total Revenue
Total Revenue									2,111,491	2,042,732	2,007,321
Net sales									1,974,739	1,910,953	1,866,180
Income Before Income Taxes
Income Before Income Taxes									219,052	211,122	161,591
Identifiable Assets
Identifiable Assets	1,701,902				1,472,148				1,701,902	1,472,148	1,346,391
Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization									85,619	74,434	74,850
Capital Expenditures
Capital Expenditures									112,308	91,423	61,443
Operating segments | Protective Solutions
Total Revenue
Total Revenue									513,584	529,324	540,665
Net sales									511,957	527,677	538,769
Income Before Income Taxes
Income Before Income Taxes									50,201	42,902	42,357
Identifiable Assets
Identifiable Assets	580,411				535,443				580,411	535,443	552,425
Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization									26,676	26,950	26,803
Capital Expenditures
Capital Expenditures									6,880	5,879	19,031
Eliminations
Total Revenue
Total Revenue									148,496	140,265	151,457
Eliminations | Consumer Packaging
Total Revenue
Total Revenue									5,495	3,293	5,557
Eliminations | Display and Packaging
Total Revenue
Total Revenue									4,622	3,546	2,863
Eliminations | Paper and Industrial Converted Products
Total Revenue
Total Revenue									136,752	131,779	141,141
Eliminations | Protective Solutions
Total Revenue
Total Revenue									1,627	1,647	1,896
Corporate
Total Revenue
Total Revenue									0	0	0
Net sales									0	0	0
Income Before Income Taxes
Income Before Income Taxes									(144,626)	(113,289)	(147,785)
Identifiable Assets
Identifiable Assets	$ 152,147				$ 141,485				152,147	141,485	287,497
Depreciation, Depletion and Amortization
Depreciation, Depletion and Amortization									0	0	0
Capital Expenditures
Capital Expenditures									$ 7,091	$ 8,764	$ 20,914