Investments TV Food Network (Details) - Television Food Network, G.P. - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Revenues, net	$ 1,208,357	$ 1,160,716	$ 1,099,307
Operating income	593,409	535,131	548,919
Net income	608,327	552,146	$ 561,657
Current assets	840,763	810,811
Non-current assets	150,277	168,547
Current liabilities	92,193	94,284
Non-current liabilities	$ 0	$ 138