UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flows from operating activities:
Net income	$ 188,167	$ 193,471
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	174,455	172,166
Allowance for doubtful accounts	1,209	6,927
Amortization of deferred financing costs and debt discount	2,718	3,135
Accretion of environmental liabilities	6,893	6,353
Changes in environmental liability estimates	387	1,232
Deferred income taxes	(356)	2,226
Other expense (income), net	1,167	(1,969)
Stock-based compensation	10,518	12,547
Loss on early extinguishment of debt	2,362	0
Gain on sale of business	0	(8,864)
Environmental expenditures	(16,323)	(7,028)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(5,659)	(263,584)
Inventories and supplies	(1,111)	(23,888)
Other current and non-current assets	(22,749)	(25,504)
Accounts payable	(78,139)	45,748
Other current and long-term liabilities	(27,966)	19,002
Net cash from operating activities	235,573	131,970
Cash flows used in investing activities:
Additions to property, plant and equipment	(204,298)	(148,042)
Proceeds from sale and disposal of fixed assets	2,944	3,023
Acquisitions, net of cash acquired	(120,636)	(68,766)
Proceeds from sale of business, net of transaction costs	0	17,486
Additions to intangible assets including costs to obtain or renew permits	(1,114)	(836)
Purchases of available-for-sale securities	(74,451)	(23,182)
Proceeds from sale of available-for-sale securities	50,290	32,835
Net cash used in investing activities	(347,265)	(187,482)
Cash flows used in financing activities:
Change in uncashed checks	2,392	475
Tax payments related to withholdings on vested restricted stock	(4,335)	(2,571)
Repurchases of common stock	(8,001)	(33,694)
Deferred financing costs paid	(6,346)	(321)
Payments on finance leases	(7,588)	(6,552)
Principal payments on debt	(618,975)	(8,768)
Proceeds from issuance of debt	500,000	0
Borrowing from revolving credit facility	114,000	0
Payment on revolving credit facility	(114,000)	0
Net cash used in financing activities	(142,853)	(51,431)
Effect of exchange rate change on cash	718	(1,001)
Decrease in cash and cash equivalents	(253,827)	(107,944)
Cash and cash equivalents, beginning of period	492,603	452,575
Cash and cash equivalents, end of period	238,776	344,631
Cash payments for interest and income taxes:
Interest paid	49,257	48,104
Income taxes paid, net of refunds	92,494	29,307
Non-cash investing activities:
Property, plant and equipment accrued	26,427	21,156
Remedial liability assumed in acquisition of property, plant and equipment	0	13,073
ROU assets obtained in exchange for operating lease liabilities	38,474	20,686
ROU assets obtained in exchange for finance lease liabilities	$ 13,992	$ 7,646