Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 394,096	$ 259,231	$ 348,884
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	235,482	212,930	188,049
Goodwill and intangible asset impairment	3,319	47,662	0
Non-cash interest expense, net	3,219	2,584	3,100
Non-cash stock-based compensation expense	16,447	13,527	15,656
Provision for deferred income taxes	22,160	56,209	18,277
Equity in earnings of unconsolidated affiliates	(27,367)	(23,855)	(21,328)
Gains on sales of assets, net	(13,908)	(16,052)	(5,935)
Other non-cash items, net	(2,768)	8,910	7,222
Changes in assets and liabilities, net of acquisitions:
Accounts receivable, net of allowance and contract assets	113,061	(335,201)	(417,491)
Inventories	24,051	(29,366)	36,187
Other assets, current and long-term portion	10,180	28,709	(117,091)
Accounts payable and accrued expenses	(228,142)	251,735	43,883
Contract liabilities	(52,215)	28,411	46,075
Other liabilities, current and long-term portion	52,663	24,522	(1,392)
Net cash provided by operating activities	550,278	529,956	144,096
Cash flows from investing activities:
Cash paid for acquisitions, net of cash acquired	(179,481)	(6,684)	(115,995)
Capital expenditures	(126,473)	(180,420)	(123,412)
Proceeds from sale of property and equipment	35,015	39,359	19,963
Payments for other investments	(5,589)	(39,469)	(77,105)
Proceeds from other investments	14,705	5,415	23,801
Net cash used in investing activities	(261,823)	(181,799)	(272,748)
Cash flows from financing activities:
Proceeds from credit facilities	3,025,927	3,418,232	2,699,047
Repayments of credit facilities	3,126,595	3,359,521	2,457,293
Repayments of other borrowings, net	(12,438)	(17,427)	(3,350)
Payments of finance lease obligations	(88,341)	(72,167)	(67,740)
Payments of acquisition-related contingent consideration	34,267	15,929	6,676
Proceeds from (distributions to) non-controlling interests	583	(559)	(22,728)
Proceeds from stock-based awards	4,655	4,047	3,104
Payments for stock-based awards	(45)	(3,821)	(6,189)
Repurchases of common stock	(5,652)	(313,949)	(1,552)
Other financing activities, net	(8,458)	0	(6,301)
Net cash (used in) provided by financing activities	(244,631)	(361,094)	130,322
Effect of currency translation on cash	181	33	(111)
Net increase (decrease) in cash and cash equivalents	44,005	(12,904)	1,559
Cash and cash equivalents - beginning of period	27,422	40,326	38,767
Cash and cash equivalents - end of period	71,427	27,422	40,326
Supplemental cash flow information:
Interest paid	84,971	81,230	59,157
Income tax payments (refunds), net	106,248	(21,450)	78,653
Supplemental disclosure of non-cash information:
Additions to property and equipment from finance leases	$ 206,156	$ 75,545	$ 150,055