Depreciation and Amortization - Depreciation and Amortization Expense Excluded from Operating Expenses in its Condensed Consolidated Statements of Income and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 84,300	$ 61,237	$ 205,671	$ 187,548
Direct advertising expenses
Property, Plant and Equipment [Line Items]
Depreciation and amortization	80,068	57,556	192,816	176,395
General and administrative expenses
Property, Plant and Equipment [Line Items]
Depreciation and amortization	1,068	1,126	3,338	3,558
Corporate expenses
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 3,164	$ 2,555	$ 9,517	$ 7,595