UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities:
Net income	$ 193,471	$ 88,811
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	172,166	143,755
Allowance for doubtful accounts	6,927	2,109
Amortization of deferred financing costs and debt discount	3,135	1,806
Accretion of environmental liabilities	6,353	5,826
Changes in environmental liability estimates	1,232	445
Deferred income taxes	2,226	1,912
Other (income) expense, net	(1,969)	2,708
Stock-based compensation	12,547	6,785
Gain on sale of business	(8,864)	0
Environmental expenditures	(7,028)	(6,594)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(263,584)	(51,285)
Inventories and supplies	(23,888)	765
Other current and non-current assets	(25,504)	(12,043)
Accounts payable	45,748	49,880
Other current and long-term liabilities	19,002	30,552
Net cash from operating activities	131,970	265,432
Cash flows used in investing activities:
Additions to property, plant and equipment	(148,042)	(91,988)
Proceeds from sale and disposal of fixed assets	3,023	3,479
Acquisitions, net of cash acquired	(68,766)	(22,918)
Proceeds from sale of business, net of transaction costs	17,486	0
Additions to intangible assets including costs to obtain or renew permits	(836)	(1,750)
Proceeds from sale of available-for-sale securities	32,835	70,526
Purchases of available-for-sale securities	(23,182)	(89,689)
Net cash used in investing activities	(187,482)	(132,340)
Cash flows used in financing activities:
Change in uncashed checks	475	(2,895)
Tax payments related to withholdings on vested restricted stock	(2,571)	(4,739)
Repurchases of common stock	(33,694)	(45,409)
Deferred financing costs paid	(321)	(146)
Payments on finance leases	(6,552)	(3,577)
Principal payments on debt	(8,768)	(3,768)
Net cash used in financing activities	(51,431)	(60,534)
Effect of exchange rate change on cash	(1,001)	3,915
(Decrease) increase in cash and cash equivalents	(107,944)	76,473
Cash and cash equivalents, beginning of period	452,575	519,101
Cash and cash equivalents, end of period	344,631	595,574
Cash payments for interest and income taxes:
Interest paid	48,104	34,164
Income taxes paid, net of refunds	29,307	32,519
Non-cash investing activities:
Property, plant and equipment accrued	21,156	8,807
Remedial liability assumed in acquisition of property, plant and equipment	13,073	0
ROU assets obtained in exchange for operating lease liabilities	20,686	5,774
ROU assets obtained in exchange for finance lease liabilities	$ 7,646	$ 18,704