Leases - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases Disclosure [Line Items]
Rent expense under all operating leases	$ 530,748	$ 478,531	$ 440,601
Net book value of property and equipment under capital leases	$ 257,772	$ 263,438
Minimum
Leases Disclosure [Line Items]
Facilities leased under non-cancellable operating leases term range	5 years
Facilities leased under non-cancellable operating leases renewal option range	5 years
Maximum
Leases Disclosure [Line Items]
Facilities leased under non-cancellable operating leases term range	15 years
Facilities leased under non-cancellable operating leases renewal option range	10 years