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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	$ 51,933	$ 48,725	$ 103,422	$ 97,955
Direct Advertising Expenses [Member]
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	48,267	44,805	96,065	89,890
General and Administrative Expenses [Member]
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	902	834	1,783	1,557
Corporate Expenses [Member]
Depreciation and Amortization Expense [Line Items]
Depreciation and amortization	$ 2,764	$ 3,086	$ 5,574	$ 6,508