Integration and reorganization costs and impairments of property, plant and equipment - Severance Related Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 29, 2019	Sep. 30, 2020	Sep. 29, 2019
Restructuring Cost and Reserve
Severance related expenses	$ 13,417	$ 3,136	$ 73,978	$ 13,213
Severance
Restructuring Cost and Reserve
Severance related expenses	7,282	1,928	54,803	8,221
Operating Segments | Publishing | Severance
Restructuring Cost and Reserve
Severance related expenses	3,983	1,489	35,401	6,145
Operating Segments | Marketing Solutions | Severance
Restructuring Cost and Reserve
Severance related expenses	1,196	431	5,333	1,167
Corporate and Other | Severance
Restructuring Cost and Reserve
Severance related expenses	$ 2,103	$ 8	$ 14,069	$ 909