Aggregate Net Purchase Price Allocation to Assets and Liabilities based on Estimated Fair Values (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 3,825,157	$ 3,784,106	$ 3,596,114
2016 Acquisitions of Assets and Businesses
Business Acquisition [Line Items]
Working capital, net		6,680
Property & equipment		343,846
Goodwill		234,658
Other assets		19,910
Income tax assets, net of deferred tax liabilities		11,551
Debt		(152)
Noncontrolling interest		(2,690)
Cash paid for acquisitions		$ 613,803
2015 Acquisitions of Assets and Businesses
Business Acquisition [Line Items]
Working capital, net			(7,000)
Property & equipment			116,000
Goodwill			319,000
Other assets			128,000
Income tax assets, net of deferred tax liabilities			(22,000)
Cash paid for acquisitions			$ 534,000