Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash Flows from Operating Activities:
Net income	$ 459,380	$ 400,915
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation & amortization	222,716	223,910
Stock-based compensation expense	34,716	29,053
Gain on sale of assets and businesses	(2,513)	0
Changes in assets & liabilities, net of effects from acquisitions and dispositions:
Accounts receivable	(64,055)	941
Accrued interest	199	211
Accrued and deferred income taxes	(42,540)	(5,529)
Other working capital accounts	8,977	(93,715)
Other assets and deferred charges	(14,144)	(19,723)
Other	18,876	(23,411)
Accrued insurance expense, net of commercial premiums paid	46,255	58,903
Payments made in settlement of self-insurance claims	(38,606)	(37,759)
Net cash provided by operating activities	629,261	533,796
Cash Flows from Investing Activities:
Property and equipment additions, net of disposals	(370,252)	(262,452)
Acquisition of property and businesses	(20,931)	(19,610)
Proceeds received from sales of assets and businesses	13,502	0
Costs incurred for purchase and implementation of information technology applications	(24,087)	(19,448)
Decrease (increase) in capital reserves of commercial insurance subsidiary	100	(3,000)
Investment in, and advances to, joint venture	(14,059)	0
Net cash used in investing activities	(415,727)	(304,510)
Cash Flows from Financing Activities:
Reduction of long-term debt	(82,470)	(45,675)
Additional borrowings	30,500	21,600
Financing costs	(754)	0
Repurchase of common shares	(134,784)	(147,463)
Dividends paid	(18,804)	(19,280)
Issuance of common stock	4,959	4,927
Profit distributions to noncontrolling interests	(7,914)	(11,430)
Net cash used in financing activities	(209,267)	(197,321)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(1,138)	938
Increase in cash, cash equivalents and restricted cash	3,129	32,903
Cash, cash equivalents and restricted cash, beginning of period	167,297	121,950
Cash, cash equivalents and restricted cash, end of period	170,426	154,853
Supplemental Disclosures of Cash Flow Information:
Interest paid	70,890	66,765
Income taxes paid, net of refunds	182,130	216,214
Noncash purchases of property and equipment	$ 91,742	$ 63,089