Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 112,457	$ 116,885	$ 254,334	$ 209,774
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	95,366	71,397	262,132	182,173
Amortization of intangible assets	23,352	11,200	54,522	28,384
Non-cash interest expense, net			2,342	2,201
Non-cash stock-based compensation expense			17,673	15,538
Provision for deferred income taxes			439	7,947
Equity in earnings of unconsolidated affiliates	(8,714)	(7,445)	(23,585)	(22,092)
Gains on sales of assets, net			(10,704)	(12,874)
Other non-cash items, net			(8,218)	23,046
Changes in assets and liabilities, net of acquisitions:
Accounts receivable			(59,665)	(49,802)
Contract assets			(109,399)	10,637
Inventories			11,968	15,645
Other assets, current and long-term portion			(8,998)	38,729
Accounts payable and accrued expenses			134,487	109,689
Contract liabilities			(7,478)	160,648
Other liabilities, current and long-term portion			(10,753)	(36,467)
Net cash provided by operating activities			499,097	683,176
Cash flows from investing activities:
Cash paid for acquisitions, net of cash acquired			(604,907)	(11,251)
Capital expenditures			(132,348)	(183,725)
Proceeds from sale of property and equipment			25,465	29,744
Payments for other investments			(7,111)	(17,436)
Proceeds from other investments			557	648
Other investing activities, net			1,650	4,843
Net cash used in investing activities			(716,694)	(177,177)
Cash flows from financing activities:
Proceeds from credit facilities			795,414	1,415,426
Repayments of credit facilities			(606,575)	(1,725,845)
Proceeds from issuance of 4.50% senior notes			0	600,000
Repayments of 4.875% senior notes			0	(400,000)
Payments of finance lease obligations			(117,437)	(92,260)
Payments of acquisition-related contingent consideration			(21,675)	(10,097)
Payments to non-controlling interests, including acquisition of interests and distributions			(8,965)	(719)
Proceeds from stock-based awards			0	5,483
Payments for stock-based awards			(3,795)	(614)
Repurchases of common stock			0	(120,228)
Other financing activities, net			(2,503)	(11,128)
Net cash provided by (used in) financing activities			34,464	(339,982)
Effect of currency translation on cash			(61)	730
Net (decrease) increase in cash and cash equivalents			(183,194)	166,747
Cash and cash equivalents - beginning of period			423,118	71,427	$ 71,427
Cash and cash equivalents - end of period	$ 239,924	$ 238,174	239,924	238,174	$ 423,118
Supplemental cash flow information:
Interest paid			49,133	57,098
Income tax payments, net of refunds			62,720	12,091
Supplemental disclosure of non-cash information:
Additions to property and equipment from finance leases			$ 128,337	$ 86,083