UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net income	$ 279,507	$ 329,270
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	267,425	260,560
Allowance for doubtful accounts	2,620	6,684
Amortization of deferred financing costs and debt discount	4,036	4,734
Accretion of environmental liabilities	10,281	9,599
Changes in environmental liability estimates	3,258	2,105
Deferred income taxes	(356)	2,226
Other expense (income), net	833	(2,073)
Stock-based compensation	14,809	20,375
Loss on early extinguishment of debt	2,362	0
Gain on sale of business	0	(8,864)
Environmental expenditures	(24,064)	(9,720)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(46,445)	(293,562)
Inventories and supplies	12,691	(44,324)
Other current and non-current assets	(18,190)	(12,600)
Accounts payable	(40,013)	52,979
Other current and long-term liabilities	(13,062)	40,153
Net cash from operating activities	455,692	357,542
Cash flows used in investing activities:
Additions to property, plant and equipment	(311,906)	(244,547)
Proceeds from sale and disposal of fixed assets	5,129	5,118
Acquisitions, net of cash acquired	(119,596)	(73,568)
Proceeds from sale of business, net of transaction costs	750	16,811
Additions to intangible assets including costs to obtain or renew permits	(1,507)	(1,094)
Purchases of available-for-sale securities	(104,329)	(36,418)
Proceeds from sale of available-for-sale securities	84,390	51,736
Net cash used in investing activities	(447,069)	(281,962)
Cash flows used in financing activities:
Change in uncashed checks	3,004	887
Tax payments related to withholdings on vested restricted stock	(10,886)	(6,214)
Repurchases of common stock	(18,000)	(44,182)
Deferred financing costs paid	(6,371)	(410)
Payments on finance leases	(11,594)	(9,538)
Principal payments on debt	(621,475)	(13,152)
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	(165,322)	(72,609)
Effect of exchange rate change on cash	61	(6,523)
Decrease in cash and cash equivalents	(156,638)	(3,552)
Cash and cash equivalents, beginning of period	492,603	452,575
Cash and cash equivalents, end of period	335,965	449,023
Cash payments for interest and income taxes:
Interest paid	100,813	86,407
Income taxes paid, net of refunds	107,328	53,183
Non-cash investing activities:
Property, plant and equipment accrued	29,127	23,726
Remedial liability assumed in acquisition of property, plant and equipment	0	8,092
ROU assets obtained in exchange for operating lease liabilities	61,741	39,899
ROU assets obtained in exchange for finance lease liabilities	$ 26,317	$ 11,263