Acquisitions and Dispositions - WLWC-TV - Additional Information (Details) - USD ($)	Oct. 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill		$ 2,142,846,000	$ 473,304,000	$ 451,662,000
WLWC [Member]
Business Acquisition [Line Items]
Acquisition date	Oct. 02, 2017
Cash paid in business acquisition	$ 4,100,000
Goodwill	$ 0
Network affiliation agreements useful life	15 years