Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 368,113	$ 302,726	$ 283,395	$ 254,191	$ 261,746	$ 200,509	$ 216,242	$ 198,475	$ 1,208,425	$ 876,972	$ 874,451
Core Advertising Revenue
Disaggregation of Revenue [Line Items]
Total operating revenues									696,449	555,228	507,987
Political Advertising Revenue
Disaggregation of Revenue [Line Items]
Total operating revenues									139,600	8,651	100,761
Retransmission revenue
Disaggregation of Revenue [Line Items]
Total operating revenues									304,402	259,712	220,723
Other Revenue
Disaggregation of Revenue [Line Items]
Total operating revenues									$ 67,974	$ 53,381	$ 44,980