UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income	$ 88,811	$ 40,595
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	143,755	147,027
Allowance for doubtful accounts	2,109	9,006
Amortization of deferred financing costs and debt discount	1,806	1,787
Accretion of environmental liabilities	5,826	5,327
Changes in environmental liability estimates	445	5,607
Deferred income taxes	1,912	0
Other expense, net	2,708	2,865
Stock-based compensation	6,785	6,077
Loss on sale of businesses	0	3,258
Environmental expenditures	(6,594)	(6,104)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(51,285)	67,540
Inventories and supplies	765	(9,024)
Other current and non-current assets	(12,043)	(25,840)
Accounts payable	49,880	(82,134)
Other current and long-term liabilities	30,552	7,499
Net cash from operating activities	265,432	173,486
Cash flows used in investing activities:
Additions to property, plant and equipment	(91,988)	(125,721)
Proceeds from sale and disposal of fixed assets	3,479	3,101
Acquisitions, net of cash acquired	(22,918)	(8,877)
Proceeds from sale of businesses, net of transactional costs	0	7,753
Additions to intangible assets including costs to obtain or renew permits	(1,750)	(1,242)
Proceeds from sale of available-for-sale securities	70,526	28,851
Purchases of available-for-sale securities	(89,689)	(45,550)
Net cash used in investing activities	(132,340)	(141,685)
Cash flows (used in) from financing activities:
Change in uncashed checks	(2,895)	(1,689)
Tax payments related to withholdings on vested restricted stock	(4,739)	(3,395)
Repurchases of common stock	(45,409)	(17,341)
Deferred financing costs paid	(146)	0
Payments on finance leases	(3,577)	(1,790)
Principal payments on debt	(3,768)	(3,768)
Borrowing from revolving credit facility	0	150,000
Payment on revolving credit facility	0	(75,000)
Net cash (used in) from financing activities	(60,534)	47,017
Effect of exchange rate change on cash	3,915	(3,443)
Increase in cash and cash equivalents	76,473	75,375
Cash and cash equivalents, beginning of period	519,101	371,991
Cash and cash equivalents, end of period	595,574	447,366
Cash payments for interest and income taxes:
Interest paid	34,164	38,327
Income taxes paid, net of refunds	32,519	1,478
Non-cash investing activities:
Property, plant and equipment accrued	8,807	7,421
ROU assets obtained in exchange for operating lease liabilities	5,774	16,216
ROU assets obtained in exchange for finance lease liabilities	$ 18,704	$ 16,452