Discontinued operations - Depreciation, Amortization and Capital Expenditures (Details) - Discontinued Operations, Disposed of by Sale - Digital - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation	$ 0	$ 19,569	$ 34,162
Amortization of intangible assets	0	40,300	91,696
Capital expenditures	0	37,441	51,581
Payments for acquisitions, net of cash acquired	$ 0	$ 0	$ 206,077