Segment Data - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 Segment Station	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	3
Percentage of revenue generated from outside the United States	7.00%	0.00%	0.00%
Television
Segment Reporting Information [Line Items]
Number of stations owned	55
Radio
Segment Reporting Information [Line Items]
Number of stations owned	49
Advertisements and Syndicates Radio Programming | Minimum
Segment Reporting Information [Line Items]
Number of stations owned	300