Goodwill and Other Intangible Assets - Carrying Amount of Goodwill (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 01, 2017
Goodwill [Line Items]
Goodwill	$ 70,557,000	$ 50,081,000	$ 50,081,000
Acquisition	20,476,000
Television
Goodwill [Line Items]
Goodwill	40,549,000	35,912,000	35,912,000
Acquisition	4,637,000
Impairment	0	0	0
Radio
Goodwill [Line Items]
Goodwill	0	0
Digital
Goodwill [Line Items]
Goodwill	30,008,000	$ 14,169,000	$ 14,169,000	$ 30,000,000
Acquisition	15,839,000
Impairment	$ 0