Related-Party Transactions - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Agreement Market shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Number of Class A common stock shares converted | shares	1
Retransmission consent revenue	$ 31.4	$ 29.6
Fees paid for carriage of programming	$ 0.0
Univision
Related Party Transaction [Line Items]
Number of marketing and sales agreements | Agreement	2
Number of markets involved in sales and marketing | Market	6
Common stock percentage held by Univision	10.00%
Retransmission consent revenue	$ 30.0	27.8
Accounts receivable from third parties	$ 3.9	$ 3.2	$ 3.0
UniMas
Related Party Transaction [Line Items]
Affiliate advertising minutes per hour for which entity has right to sell	4 minutes 30 seconds
Minimum | Univision
Related Party Transaction [Line Items]
Affiliate advertising minutes per hour for which entity has right to sell	4 minutes