SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Benefit (charge) within operating expense	$ (9,000)	$ 9,000	$ 4,000
Accounts receivable allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	14,915	15,560	16,388
Charged to Earnings	12,335	13,118	11,172
Transferred from (to) Other Accounts	0	0	0
Deductions	13,403	13,763	12,000
Balance at End of Period	13,847	14,915	15,560
Self-insurance accruals
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	336,901	311,821	298,853
Charged to Earnings	327,306	324,673	295,399
Transferred from (to) Other Accounts	74,153	71,703	68,999
Deductions	389,748	371,296	351,430
Balance at End of Period	348,612	336,901	311,821
Valuation allowance on deferred tax assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	16,387	14,991	24,742
Charged to Earnings	2,213	98	(1,150)
Transferred from (to) Other Accounts	0	0	0
Deductions	67	(1,298)	8,601
Balance at End of Period	$ 18,667	$ 16,387	$ 14,991