Segment Information - Disaggregation of Revenue Generating Activities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 254,191	$ 198,475
Core advertising
Disaggregation of Revenue [Line Items]
Total operating revenues	166,553	118,855
Political advertising
Disaggregation of Revenue [Line Items]
Total operating revenues	2,584	1,041
Retransmission
Disaggregation of Revenue [Line Items]
Total operating revenues	71,060	66,211
Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 13,994	$ 12,368