CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income	$ 377,856	$ 411,744	$ 203,247
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	365,761	347,594	298,135
Allowance for doubtful accounts	5,956	7,783	8,018
Amortization of deferred financing costs and debt discount	5,309	6,301	4,245
Accretion of environmental liabilities	13,667	12,943	11,745
Changes in environmental liability estimates	4,828	8,272	2,979
Deferred income taxes	12,685	17,549	1,482
Other (income) expense, net	(2,315)	(2,472)	515
Stock-based compensation	20,703	26,844	18,839
Loss on early extinguishment of debt	2,880	422	0
Gain on sale of business	0	(8,864)	0
Environmental expenditures	(28,960)	(13,946)	(15,506)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	2,453	(201,087)	(96,551)
Inventories and supplies	(4,312)	(74,547)	(31,689)
Other current and non-current assets	(22,645)	(17,303)	9,268
Accounts payable	(27,425)	74,460	108,398
Other current and long-term liabilities	8,111	30,521	22,872
Net cash from operating activities	734,552	626,214	545,997
Cash flows used in investing activities:
Additions to property, plant and equipment	(422,300)	(345,056)	(241,856)
Proceeds from sale and disposal of fixed assets	9,650	8,779	22,156
Acquisitions, net of cash acquired	(119,596)	(86,278)	(1,253,232)
Proceeds from sale of business, net of transaction costs	750	16,811	0
Additions to intangible assets including costs to obtain or renew permits	(2,649)	(1,966)	(3,848)
Purchases of available-for-sale securities	(158,264)	(49,845)	(129,234)
Proceeds from sale of available-for-sale securities	117,359	68,611	98,412
Net cash used in investing activities	(575,050)	(388,944)	(1,507,602)
Cash flows (used in) from financing activities:
Change in uncashed checks	2,759	552	(1,806)
Tax payments related to withholdings on vested restricted stock	(13,838)	(8,801)	(10,805)
Repurchases of common stock	(51,164)	(50,183)	(54,410)
Deferred financing costs paid	(6,736)	(410)	(13,737)
Payments on finance leases	(15,937)	(12,821)	(8,458)
Principal payments on debt	(623,975)	(115,652)	(7,535)
Proceeds from issuance of debt, net of discount	500,000	0	995,000
Borrowing from revolving credit facility	114,000	0	0
Payment on revolving credit facility	(114,000)	0	0
Net cash (used in) from financing activities	(208,891)	(187,315)	898,249
Effect of exchange rate change on cash	1,484	(9,927)	(3,170)
(Decrease) increase in cash and cash equivalents	(47,905)	40,028	(66,526)
Cash and cash equivalents, beginning of year	492,603	452,575	519,101
Cash and cash equivalents, end of year	444,698	492,603	452,575
Cash payments for interest and income taxes:
Interest paid	114,560	105,643	73,440
Income taxes paid, net of refunds	132,314	78,526	65,192
Non-cash investing activities:
Property, plant and equipment accrued	52,376	30,950	19,264
Remedial liability assumed in acquisition of property, plant and equipment	$ 0	$ 8,092	$ 0