Basis and Summary of Significant Accounting Policies - Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Accounts Payable	$ 98,460	$ 80,821
Accrued Insurance Costs	42,268	41,680
Accrued Salaries and Benefits	49,849	46,511
Accrued Real Estate and Sales Taxes	31,184	31,054
Deferred Rent	27,454	29,912
Other Accrued Expenses and Liabilities	69,181	74,832
Accounts Payable and Accrued Expenses	$ 318,396	$ 304,810