Integration and reorganization costs and asset impairments - Facility Consolidation Charges and Accelerated Depreciation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Restructuring Cost and Reserve
Restructuring provision included in integration and reorganization costs	$ 8,444	$ 32,306	$ 21,848	$ 60,560
Facility Closing
Restructuring Cost and Reserve
Restructuring provision included in integration and reorganization costs	7,315	6,564	13,622	13,039
Operating Segments | Publishing | Facility Closing
Restructuring Cost and Reserve
Restructuring provision included in integration and reorganization costs	(1,602)	1,477	(1,055)	2,509
Operating Segments | Digital Marketing Solutions | Facility Closing
Restructuring Cost and Reserve
Restructuring provision included in integration and reorganization costs	228	209	451	214
Corporate and other | Facility Closing
Restructuring Cost and Reserve
Restructuring provision included in integration and reorganization costs	$ 8,689	$ 4,878	$ 14,226	$ 10,316