UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net income	$ 154,254	$ 95,505
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	215,206	221,497
Allowance for doubtful accounts	7,186	10,441
Amortization of deferred financing costs and debt discount	2,718	2,688
Accretion of environmental liabilities	8,625	8,149
Changes in environmental liability estimates	341	9,050
Deferred income taxes	5,202	0
Other expense, net	2,509	597
Stock-based compensation	12,786	12,739
Loss on sale of businesses	0	3,376
Environmental expenditures	(12,223)	(8,816)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(113,601)	23,969
Inventories and supplies	(12,882)	(9,554)
Other current and non-current assets	(10,785)	(19,320)
Accounts payable	86,974	(63,898)
Other current and long-term liabilities	21,916	31,009
Net cash from operating activities	368,226	317,432
Cash flows used in investing activities:
Additions to property, plant and equipment	(146,654)	(150,357)
Proceeds from sale and disposal of fixed assets	16,424	7,307
Acquisitions, net of cash acquired	(22,819)	(8,839)
Proceeds from sale of businesses, net of transactional costs	0	7,712
Additions to intangible assets including costs to obtain or renew permits	(2,659)	(1,863)
Proceeds from sale of available-for-sale securities	83,226	39,141
Purchases of available-for-sale securities	(96,785)	(53,397)
Net cash used in investing activities	(169,267)	(160,296)
Cash flows used in financing activities:
Change in uncashed checks	(4,323)	381
Tax payments related to withholdings on vested restricted stock	(7,383)	(4,407)
Repurchases of common stock	(48,409)	(39,542)
Deferred financing costs paid	(150)	0
Payments on finance leases	(5,845)	(2,755)
Principal payments on debt	(5,652)	(5,652)
Borrowing from revolving credit facility	0	150,000
Payment on revolving credit facility	0	(150,000)
Net cash used in financing activities	(71,762)	(51,975)
Effect of exchange rate change on cash	365	(1,446)
Increase in cash and cash equivalents	127,562	103,715
Cash and cash equivalents, beginning of period	519,101	371,991
Cash and cash equivalents, end of period	646,663	475,706
Cash payments for interest and income taxes:
Interest paid	61,807	66,000
Income taxes paid, net of refunds	48,202	14,195
Non-cash investing activities:
Property, plant and equipment accrued	11,561	11,732
ROU assets obtained in exchange for operating lease liabilities	18,528	19,993
ROU assets obtained in exchange for finance lease liabilities	$ 18,704	$ 28,333