UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 21,736	$ 11,572
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	72,163	74,533
Allowance for doubtful accounts	2,446	4,700
Amortization of deferred financing costs and debt discount	900	891
Accretion of environmental liabilities	2,953	2,561
Changes in environmental liability estimates	275	3,470
Deferred income taxes	(39)	0
Other expense, net	1,228	2,365
Stock-based compensation	3,480	3,291
Loss on sale of businesses	0	3,074
Environmental expenditures	(3,011)	(3,435)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(9,703)	(24,960)
Inventories and supplies	(747)	(7,024)
Other current and non-current assets	(9,956)	8,714
Accounts payable	22,179	(5,169)
Other current and long-term liabilities	(904)	(40,902)
Net cash from operating activities	103,000	33,681
Cash flows used in investing activities:
Additions to property, plant and equipment	(41,913)	(82,767)
Proceeds from sale and disposal of fixed assets	1,204	2,150
Acquisitions, net of cash acquired	(22,918)	0
Proceeds from sale of businesses, net of transactional costs	0	7,856
Additions to intangible assets including costs to obtain or renew permits	(505)	(448)
Proceeds from sale of available-for-sale securities	20,375	12,180
Purchases of available-for-sale securities	(42,980)	(32,058)
Net cash used in investing activities	(86,737)	(93,087)
Cash flows (used in) from financing activities:
Change in uncashed checks	(6,662)	(1,775)
Tax payments related to withholdings on vested restricted stock	(3,719)	(2,224)
Repurchases of common stock	(26,546)	(17,341)
Deferred financing costs paid	(137)	0
Payments on finance leases	(1,672)	(329)
Principal payments on debt	(1,884)	(1,884)
Borrowings from revolving credit facility	0	150,000
Net cash (used in) from financing activities	(40,620)	126,447
Effect of exchange rate change on cash	1,639	(6,827)
(Decrease) increase in cash and cash equivalents	(22,718)	60,214
Cash and cash equivalents, beginning of period	519,101	371,991
Cash and cash equivalents, end of period	496,383	432,205
Cash payments for interest and income taxes:
Interest paid	27,507	30,648
Income taxes paid, net of refunds	3,599	971
Non-cash investing activities:
Property, plant and equipment accrued	5,108	12,173
ROU assets obtained in exchange for operating lease liabilities	2,305	12,410
ROU assets obtained in exchange for finance lease liabilities	$ 9,205	$ (856)