Significant Transactions - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Station	Dec. 31, 2015 USD ($)
Significant Transactions [Line Items]
Revenue from spectrum usage rights	$ 263,943	$ 10,650
Cost of revenue - television (spectrum usage rights)	12,340
FCC
Significant Transactions [Line Items]
Revenue from spectrum usage rights	263,900
Cost of revenue - television (spectrum usage rights)	$ 12,300
Television | FCC
Significant Transactions [Line Items]
Number of stations owned from spectrum usage rights | Station	4