UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 95,505	$ 73,589
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	221,497	223,328
Allowance for doubtful accounts	10,441	(745)
Amortization of deferred financing costs and debt discount	2,688	2,908
Accretion of environmental liabilities	8,149	7,624
Changes in environmental liability estimates	9,050	(585)
Deferred income taxes	0	(973)
Other expense (income), net	597	(1,992)
Stock-based compensation	12,739	14,664
Loss on sale of businesses	3,376	0
Loss on early extinguishment of debt	0	6,119
Environmental expenditures	(8,816)	(12,804)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	23,969	(31,408)
Inventories and supplies	(9,554)	(11,982)
Other current and non-current assets	(19,320)	(5,425)
Accounts payable	(63,898)	3,035
Other current and long-term liabilities	31,009	19,322
Net cash from operating activities	317,432	284,675
Cash flows used in investing activities:
Additions to property, plant and equipment	(150,357)	(174,533)
Proceeds from sale and disposal of fixed assets	7,307	8,948
Acquisitions, net of cash acquired	(8,839)	(29,479)
Proceeds from sale of businesses, net of transactional costs	7,712	0
Additions to intangible assets including costs to obtain or renew permits	(1,863)	(2,896)
Proceeds from sale of available-for-sale securities	39,141	41,612
Purchases of available-for-sale securities	(53,397)	(30,761)
Net cash used in investing activities	(160,296)	(187,109)
Cash flows used in financing activities:
Change in uncashed checks	381	(3,516)
Tax payments related to withholdings on vested restricted stock	(4,407)	(5,505)
Repurchases of common stock	(39,542)	(16,390)
Deferred financing costs paid	0	(10,053)
Premiums paid on early extinguishment of debt	0	(2,689)
Payments on finance leases	(2,755)	(327)
Principal payments on debt	(5,652)	(850,652)
Issuance of unsecured senior notes	0	845,000
Borrowing from revolving credit facility	150,000	0
Payment on revolving credit facility	(150,000)	0
Net cash used in financing activities	(51,975)	(44,132)
Effect of exchange rate change on cash	(1,446)	2,292
Increase in cash and cash equivalents	103,715	55,726
Cash and cash equivalents, beginning of period	371,991	226,507
Cash and cash equivalents, end of period	475,706	282,233
Cash payments for interest and income taxes:
Interest paid	66,000	52,440
Income taxes paid, net of refunds	14,195	23,797
Non-cash investing activities:
Property, plant and equipment accrued	11,732	14,875
ROU assets obtained in exchange for operating lease liabilities	19,993	8,008
ROU assets obtained in exchange for finance lease liabilities	$ 28,333	$ 31,011