Segment Data - Separate Financial Data for Each of Company's Operating Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue from advertising and retransmission consent									$ 272,091	$ 258,514	$ 243,484
Revenue from spectrum usage rights (television)									263,943		10,650
Net revenue	$ 73,460	$ 334,555	$ 70,509	$ 57,510	$ 70,291	$ 65,281	$ 64,829	$ 58,113	536,034	258,514	254,134
Cost of revenue - television (spectrum usage rights)									12,340
Cost of revenue - digital media									32,206	9,536	7,242
Direct operating expenses									119,283	113,439	110,323
Selling, general and administrative expenses									49,116	46,798	42,815
Depreciation and amortization									16,411	15,342	15,989
Operating income (loss)									278,391	48,856	55,245
Corporate expenses									27,937	24,543	22,520
Foreign currency (gain) loss									350
Capital expenditures									12,688	9,308	13,548
Total assets	765,967				517,921				$ 765,967	$ 517,921	524,962
Percentage change in revenue from advertising and retransmission consent									5.00%	6.00%
Percentage change in net revenue									107.00%	2.00%
Percentage change in direct operating expenses									5.00%	3.00%
Percentage change in selling, general and administrative expenses									5.00%	9.00%
Percentage change in depreciation and amortization									7.00%	(4.00%)
Percentage change in segment operating profit (loss)									318.00%	(6.00%)
Percentage change in corporate expenses									14.00%	9.00%
Percentage change in operating income (loss)									470.00%	(12.00%)
Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)									$ 306,678	$ 73,399	77,765
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Corporate expenses									27,937	24,543	22,520
Television
Segment Reporting Information [Line Items]
Revenue from advertising and retransmission consent									148,059	159,523	148,431
Direct operating expenses									59,454	62,020	60,125
Selling, general and administrative expenses									22,276	21,591	20,541
Depreciation and amortization									9,760	10,659	11,569
Capital expenditures									10,945	5,744	7,631
Total assets	556,942				363,852				$ 556,942	$ 363,852	367,869
Percentage change in revenue from advertising and retransmission consent									(7.00%)	0.00%
Percentage change in direct operating expenses									(4.00%)	3.00%
Percentage change in selling, general and administrative expenses									3.00%	5.00%
Percentage change in depreciation and amortization									(8.00%)	(8.00%)
Percentage change in segment operating profit (loss)									372.00%	(2.00%)
Television | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)									$ 308,172	$ 65,253	66,846
Radio
Segment Reporting Information [Line Items]
Revenue from advertising and retransmission consent									66,934	75,847	76,161
Direct operating expenses									44,572	44,949	43,351
Selling, general and administrative expenses									18,743	20,441	18,619
Depreciation and amortization									2,673	3,269	3,224
Capital expenditures									1,679	3,287	5,532
Total assets	126,248				129,825				$ 126,248	$ 129,825	132,395
Percentage change in revenue from advertising and retransmission consent									(12.00%)	0.00%
Percentage change in direct operating expenses									(1.00%)	4.00%
Percentage change in selling, general and administrative expenses									(8.00%)	10.00%
Percentage change in depreciation and amortization									(18.00%)	1.00%
Percentage change in segment operating profit (loss)									(87.00%)	(34.00%)
Radio | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)									$ 946	$ 7,188	10,967
Digital
Segment Reporting Information [Line Items]
Revenue from advertising and retransmission consent									57,098	23,144	18,892
Direct operating expenses									15,257	6,470	6,847
Selling, general and administrative expenses									8,097	4,766	3,655
Depreciation and amortization									3,978	1,414	1,196
Capital expenditures									64	277	385
Total assets	$ 82,777				$ 24,244				$ 82,777	$ 24,244	24,698
Percentage change in revenue from advertising and retransmission consent									147.00%	23.00%
Percentage change in cost of revenue									238.00%	32.00%
Percentage change in direct operating expenses									136.00%	(6.00%)
Percentage change in selling, general and administrative expenses									70.00%	30.00%
Percentage change in depreciation and amortization									181.00%	18.00%
Digital | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)									$ (2,440)	$ 958	$ (48)