Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,221,560	$ 1,086,160
Less: accumulated depreciation	(432,123)	(387,798)
Total property and equipment, net	789,437	698,362
Buildings
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	634,061	548,232
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	256,509	236,634
Software
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	151,890	134,321
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	117,806	108,702
Computers
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 61,294	$ 58,271