Depreciation and Amortization - Depreciation and Amortization Expense Excluded from Operating Expenses in its Statements of Income and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	$ 49,307	$ 46,441	$ 152,729	$ 144,396
Direct Advertising Expenses [Member]
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	46,163	42,764	142,228	132,655
General and Administrative Expenses [Member]
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	900	738	2,683	2,294
Corporate Expenses [Member]
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	$ 2,244	$ 2,939	$ 7,818	$ 9,447