UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from (used in) operating activities:
Net income	$ 72,401	$ 45,314
Adjustments to reconcile net income to net cash from (used in) operating activities:
Depreciation and amortization	84,758	84,298
Allowance for doubtful accounts	1,398	3,619
Amortization of deferred financing costs and debt discount	1,354	1,561
Accretion of environmental liabilities	3,407	3,156
Changes in environmental liability estimates	683	312
Deferred income taxes	(363)	2,226
Other income, net	(116)	(704)
Stock-based compensation	6,018	5,712
Loss on early extinguishment of debt	2,362	0
Environmental expenditures	(8,348)	(3,615)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(5,030)	(138,690)
Inventories and supplies	2,758	(13,610)
Other current and non-current assets	(17,328)	(32,924)
Accounts payable	(21,801)	43,001
Other current and long-term liabilities	(94,145)	(38,285)
Net cash from (used in) operating activities	28,008	(38,629)
Cash flows used in investing activities:
Additions to property, plant and equipment	(81,686)	(70,308)
Proceeds from sale and disposal of fixed assets	1,855	1,320
Acquisitions, net of cash acquired	(108,533)	5,000
Additions to intangible assets including costs to obtain or renew permits	(333)	(321)
Purchases of available-for-sale securities	(39,037)	(5,002)
Proceeds from sale of available-for-sale securities	29,800	10,450
Net cash used in investing activities	(197,934)	(58,861)
Cash flows used in financing activities:
Change in uncashed checks	164	(2,295)
Tax payments related to withholdings on vested restricted stock	(3,351)	(1,831)
Repurchases of common stock	(3,000)	(3,694)
Deferred financing costs paid	(6,094)	(291)
Payments on finance leases	(3,689)	(3,585)
Principal payments on debt	(616,475)	(4,384)
Proceeds from issuance of debt	500,000	0
Borrowing from revolving credit facility	114,000	0
Net cash used in financing activities	(18,445)	(16,080)
Effect of exchange rate change on cash	75	579
Decrease in cash and cash equivalents	(188,296)	(112,991)
Cash and cash equivalents, beginning of period	492,603	452,575
Cash and cash equivalents, end of period	304,307	339,584
Cash payments for interest and income taxes:
Interest paid	34,878	33,697
Income taxes paid, net of refunds	37,141	3,121
Non-cash investing activities:
Property, plant and equipment accrued	27,533	11,397
Remedial liability assumed in acquisition of property, plant and equipment	0	13,073
ROU assets obtained in exchange for operating lease liabilities	10,203	7,342
ROU assets obtained in exchange for finance lease liabilities	$ 5,153	$ 4,679