Discontinued operations - Depreciation, Amortization and Capital Expenditures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation			$ 78,929
Amortization of intangible assets			96,773
Capital expenditures			58,786
Payments for acquisitions, net of cash acquired			53,655
Digital
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation	$ 19,569	$ 34,162	28,662
Amortization of intangible assets	40,300	91,696	89,765
Capital expenditures	37,441	51,581	37,853
Payments for acquisitions, net of cash acquired	$ 0	$ 206,077	24,987
Publishing
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation			49,542
Amortization of intangible assets			7,008
Capital expenditures			20,252
Payments for acquisitions, net of cash acquired			28,668
Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation			725
Amortization of intangible assets			0
Capital expenditures			681
Payments for acquisitions, net of cash acquired			$ 0