Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 330,729	$ 322,699	$ 394,096
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	345,612	258,841	212,485
Amortization of intangible assets	77,214	38,910	22,997
Non-cash stock-based compensation expense	24,805	21,875	16,447
Provision for deferred income taxes	51,931	7,180	22,160
Equity in earnings of unconsolidated affiliates	(33,830)	(29,738)	(27,367)
Gains on sales of assets, net	(35,635)	(16,210)	(13,908)
Non-cash interest expense, net	3,171	2,988	3,219
Goodwill and intangible asset impairment	0	0	3,319
Other non-cash items, net	(12,323)	21,775	(2,768)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	149,152	87,372	(124,739)
Contract assets	49,295	63,306	237,800
Inventories	10,147	17,904	24,051
Other assets, current and long-term portion	(35,837)	20,486	10,180
Accounts payable and accrued expenses	(104,481)	94,069	(228,142)
Contract liabilities	10,603	21,326	(52,215)
Other liabilities, current and long-term portion	(37,479)	4,471	52,663
Net cash provided by operating activities	793,074	937,254	550,278
Cash flows from investing activities:
Cash paid for acquisitions, net of cash acquired	(1,244,603)	(24,971)	(179,481)
Capital expenditures	(170,066)	(213,746)	(126,473)
Proceeds from sale of property and equipment	65,287	37,077	35,015
Payments for other investments	(9,996)	(17,456)	(5,589)
Proceeds from other investments	557	648	14,705
Other investing activities, net	1,650	1,843	0
Net cash used in investing activities	(1,357,171)	(216,605)	(261,823)
Cash flows from financing activities:
Proceeds from credit facilities	1,503,372	1,434,610	3,025,927
Repayments of credit facilities	(812,103)	(1,741,067)	(3,126,595)
Proceeds from issuance of 4.50% senior notes	0	600,000	0
Repayments of 4.875% senior notes	0	(400,000)	0
Payments of finance lease obligations	(158,892)	(126,988)	(88,341)
Payments of acquisition-related contingent consideration	(21,675)	(10,097)	(34,267)
(Payments to) proceeds from non-controlling interests, including acquisition of interests	(8,965)	(719)	583
Proceeds from stock-based awards	0	7,090	4,655
Payments for stock-based awards	(6,024)	(636)	(45)
Repurchases of common stock	0	(120,228)	(5,652)
Other financing activities, net	6,229	(11,852)	(20,896)
Net cash provided by (used in) financing activities	501,942	(369,887)	(244,631)
Effect of currency translation on cash	(227)	929	181
Net (decrease) increase in cash and cash equivalents	(62,382)	351,691	44,005
Cash and cash equivalents - beginning of period	423,118	71,427	27,422
Cash and cash equivalents - end of period	360,736	423,118	71,427
Supplemental cash flow information:
Interest paid	61,815	65,016	84,971
Income taxes paid, net of refunds	69,110	64,651	106,248
Supplemental disclosure of non-cash information:
Additions to property and equipment from finance leases	$ 160,286	$ 114,221	$ 206,156