Strategic actions - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 28, 2014 USD ($)	Sep. 07, 2016 employee
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$ 3,341,198	$ 3,050,945	$ 2,626,141
Digital | Operating Segments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	1,407,619	$ 1,368,801	$ 934,275
Digital | Cars.com
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	633,000
Entity number of employees | employee				1,275
Digital | CareerBuilder
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	$ 714,000
Entity number of employees | employee				3,300
Ownership interest (as a percent)				53.00%