Acquisitions - Summary of Purchase Price Allocation (Detail) - USD ($) $ in Thousands	Jun. 11, 2018	Nov. 01, 2017	Apr. 04, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill				$ 74,292	$ 70,729	$ 50,081
Smadex
Business Acquisition [Line Items]
Purchase price consideration	$ 3,500
Accounts receivable	900
Other current assets	400
Intangible assets subject to amortization	2,000
Goodwill	3,600
Current liabilities	(2,800)
Long-term liabilities	(200)
Deferred tax	$ (400)
Headway
Business Acquisition [Line Items]
Purchase price consideration			$ 8,200
Accounts receivable			19,800
Intangible assets subject to amortization			15,900
Goodwill			16,100
Current liabilities			(23,700)
Deferred tax			$ (4,000)
KMIR-TV and KPSE-LD
Business Acquisition [Line Items]
Purchase price consideration		$ 21,000
Property and equipment		2,900
Intangible assets subject to amortization		3,600
Goodwill		4,600
FCC licenses		$ 9,900