UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net income	$ 69,832	$ 72,401
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	95,065	84,758
Allowance for doubtful accounts	1,728	1,398
Amortization of deferred financing costs and debt discount	1,329	1,354
Accretion of environmental liabilities	3,217	3,407
Changes in environmental liability estimates	917	683
Deferred income taxes	(88)	(363)
Other expense (income), net	1,141	(116)
Stock-based compensation	6,338	6,018
Loss on early extinguishment of debt	0	2,362
Environmental expenditures	(4,729)	(8,348)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(44,383)	(5,030)
Inventories and supplies	(13,572)	2,758
Other current and non-current assets	(25,918)	(17,328)
Accounts payable	(17,358)	(21,801)
Other current and long-term liabilities	(54,970)	(94,145)
Net cash from operating activities	18,549	28,008
Cash flows used in investing activities:
Additions to property, plant and equipment	(137,913)	(81,686)
Proceeds from sale and disposal of fixed assets	1,008	1,855
Acquisitions, net of cash acquired	(475,306)	(108,533)
Proceeds from sale of business, net of transaction costs	750	0
Additions to intangible assets including costs to obtain or renew permits	(534)	(333)
Purchases of available-for-sale securities	(31,228)	(39,037)
Proceeds from sale of available-for-sale securities	33,350	29,800
Net cash used in investing activities	(609,873)	(197,934)
Cash flows from (used in) financing activities:
Change in uncashed checks	7,778	164
Tax payments related to withholdings on vested restricted stock	(3,052)	(3,351)
Repurchases of common stock	(5,000)	(3,000)
Deferred financing costs paid	(4,641)	(6,094)
Payments on finance leases	(4,665)	(3,689)
Principal payments on debt	(3,776)	(616,475)
Proceeds from issuance of debt, net of discount	499,375	500,000
Borrowing from revolving credit facility	0	114,000
Net cash from (used in) financing activities	486,019	(18,445)
Effect of exchange rate change on cash	(1,568)	75
Decrease in cash and cash equivalents	(106,873)	(188,296)
Cash and cash equivalents, beginning of period	444,698	492,603
Cash and cash equivalents, end of period	337,825	304,307
Cash payments for interest and income taxes:
Interest paid	51,243	34,878
Income taxes paid, net of refunds	8,020	37,141
Non-cash investing activities:
Property, plant and equipment accrued	28,266	27,533
ROU assets obtained in exchange for operating lease liabilities	23,101	10,203
ROU assets obtained in exchange for finance lease liabilities	$ 14,519	$ 5,153