CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 411,744	$ 203,247	$ 134,837
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	347,594	298,135	292,915
Allowance for doubtful accounts	7,783	8,018	10,133
Amortization of deferred financing costs and debt discount	6,301	4,245	3,666
Accretion of environmental liabilities	12,943	11,745	11,051
Changes in environmental liability estimates	8,272	2,979	10,698
Deferred income taxes	17,549	1,482	(9,748)
Other (income) expense, net	(2,472)	515	290
Stock-based compensation	26,844	18,839	18,502
(Gain) loss on sale of businesses	(8,864)	0	3,376
Loss on early extinguishment of debt	422	0	0
Environmental expenditures	(13,946)	(15,506)	(12,401)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(201,087)	(96,551)	22,422
Inventories and supplies	(74,547)	(31,689)	(7,933)
Other current and non-current assets	(17,303)	9,268	(12,602)
Accounts payable	74,460	108,398	(80,328)
Other current and long-term liabilities	30,521	22,872	45,719
Net cash from operating activities	626,214	545,997	430,597
Cash flows used in investing activities:
Additions to property, plant and equipment	(345,056)	(241,856)	(196,256)
Proceeds from sale and disposal of fixed assets	8,779	22,156	9,623
Acquisitions, net of cash acquired	(86,278)	(1,253,232)	(8,839)
Additions to intangible assets including costs to obtain or renew permits	(1,966)	(3,848)	(2,029)
Purchases of available-for-sale securities	(49,845)	(129,234)	(70,891)
Proceeds from sale of available-for-sale securities	68,611	98,412	61,220
Proceeds from sale of businesses, net of transactional costs	16,811	0	7,712
Net cash used in investing activities	(388,944)	(1,507,602)	(199,460)
Cash flows (used in) from financing activities:
Change in uncashed checks	552	(1,806)	5,404
Tax payments related to withholdings on vested restricted stock	(8,801)	(10,805)	(5,331)
Repurchases of common stock	(50,183)	(54,410)	(74,844)
Deferred financing costs paid	(410)	(13,737)	(2,171)
Payments on finance leases	(12,821)	(8,458)	(4,469)
Principal payments on debt	(115,652)	(7,535)	(7,535)
Proceeds from issuance of debt, net of discount	0	995,000	0
Borrowings from revolving credit facility	0	0	150,000
Payments on revolving credit facility	0	0	(150,000)
Net cash (used in) from financing activities	(187,315)	898,249	(88,946)
Effect of exchange rate change on cash	(9,927)	(3,170)	4,919
Increase (decrease) in cash and cash equivalents	40,028	(66,526)	147,110
Cash and cash equivalents, beginning of year	452,575	519,101	371,991
Cash and cash equivalents, end of year	492,603	452,575	519,101
Cash payments for interest and income taxes:
Interest paid	105,643	73,440	72,535
Income taxes paid, net of refunds	78,526	65,192	53,123
Non-cash investing activities:
Property, plant and equipment accrued	30,950	19,264	3,536
Remedial liability assumed in acquisition of property, plant and equipment	$ 8,092	$ 0	$ 0