Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 116,885	$ 130,082	$ 209,774	$ 293,411
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	71,397	50,515	182,173	160,019
Amortization of intangible assets	11,200	4,681	28,384	14,152
Non-cash interest expense, net			2,201	1,691
Non-cash stock-based compensation expense			15,538	12,132
Provision for deferred income taxes			7,947	8,546
Provision for credit losses	1,900	400	14,213	1,326
Equity in earnings of unconsolidated affiliates	(7,445)	(6,966)	(22,092)	(19,778)
Gains on sales of assets, net			(12,874)	(9,627)
Other non-cash items, net			8,833	(2,841)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable, net of allowance			(49,802)	(33,522)
Contract assets			10,637	34,253
Inventories			15,645	21,293
Other assets, current and long-term portion			38,729	16,641
Accounts payable and accrued expenses			109,689	(30,641)
Contract liabilities			160,648	(52,537)
Other liabilities, current and long-term portion			(7,185)	26,876
Net cash provided by operating activities			712,458	441,394
Cash flows from investing activities:
Cash paid for acquisitions, net of cash acquired			(11,251)	(94,647)
Capital expenditures			(183,725)	(85,095)
Proceeds from sale of property and equipment			29,744	27,102
Payments for other investments			(17,436)	(5,589)
Proceeds from other investments			648	14,705
Other investing activities, net			4,843	0
Net cash used in investing activities			(177,177)	(143,524)
Cash flows from financing activities:
Proceeds from credit facilities			1,415,426	2,185,714
Repayments of credit facilities			(1,725,845)	(2,371,965)
Proceeds from issuance of 4.50% senior notes			600,000	0
Repayments of 4.875% senior notes			(400,000)	0
Repayments of other borrowings, net			(50)	(333)
Payments of finance lease obligations			(92,260)	(59,045)
Payments of acquisition-related contingent consideration			39,379	29,267
(Distributions to) proceeds from non-controlling interests			(719)	584
Proceeds from stock-based awards			5,483	3,414
Payments for stock-based awards			(614)	(34)
Repurchases of common stock			(120,228)	(5,652)
Other financing activities, net			(11,078)	(5,459)
Net cash used in financing activities			(369,264)	(282,043)
Effect of currency translation on cash			730	(154)
Net increase in cash and cash equivalents			166,747	15,673
Cash and cash equivalents - beginning of period			71,427	27,422	$ 27,422
Cash and cash equivalents - end of period	$ 238,174	$ 43,095	238,174	43,095	$ 71,427
Supplemental cash flow information:
Interest paid			57,098	73,570
Income tax payments, net of refunds			12,091	73,502
Supplemental disclosure of non-cash information:
Additions to property and equipment from finance leases			$ 86,083	$ 163,458
4.50% Senior Notes [Member] | Senior Notes [Member]
Debt instrument, interest rate (percentage)	4.50%		4.50%
4.875% Senior Notes [Member] | Senior Notes [Member]
Debt instrument, interest rate (percentage)	4.875%		4.875%