UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 40,595	$ 37,220
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	147,027	149,572
Allowance for doubtful accounts	9,006	(2,233)
Amortization of deferred financing costs and debt discount	1,787	2,000
Accretion of environmental liabilities	5,327	5,134
Changes in environmental liability estimates	5,607	(748)
Deferred income taxes	0	(1,636)
Other expense (income), net	2,865	(2,419)
Stock-based compensation	6,077	9,643
Loss on sale of businesses	3,258	0
Environmental expenditures	(6,104)	(6,134)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	67,540	(13,284)
Inventories and supplies	(9,024)	(4,129)
Other current and non-current assets	(25,840)	(10,706)
Accounts payable	(82,134)	(20,915)
Other current and long-term liabilities	7,499	(2,895)
Net cash from operating activities	173,486	138,470
Cash flows used in investing activities:
Additions to property, plant and equipment	(125,721)	(118,372)
Proceeds from sale and disposal of fixed assets	3,101	7,389
Acquisitions, net of cash acquired	(8,877)	(29,479)
Proceeds from sale of businesses, net of transactional costs	7,753	0
Additions to intangible assets including costs to obtain or renew permits	(1,242)	(1,923)
Proceeds from sale of available-for-sale securities	28,851	26,518
Purchases of available-for-sale securities	(45,550)	(24,001)
Net cash used in investing activities	(141,685)	(139,868)
Cash flows from (used in) financing activities:
Change in uncashed checks	(1,689)	(3,514)
Tax payments related to withholdings on vested restricted stock	(3,395)	(4,980)
Repurchases of common stock	(17,341)	(11,272)
Payments on finance leases	(1,790)	(259)
Principal payments on debt	(3,768)	(3,768)
Borrowing from revolving credit facility	150,000	0
Payment on revolving credit facility	(75,000)	0
Net cash from (used in) financing activities	47,017	(23,793)
Effect of exchange rate change on cash	(3,443)	3,139
Increase (decrease) in cash and cash equivalents	75,375	(22,052)
Cash and cash equivalents, beginning of period	371,991	226,507
Cash and cash equivalents, end of period	447,366	204,455
Cash payments for interest and income taxes:
Interest paid	38,327	39,369
Income taxes paid	1,478	12,697
Non-cash investing activities:
Property, plant and equipment accrued	7,421	14,103
ROU assets obtained in exchange for operating lease liabilities	16,216	5,575
ROU assets obtained in exchange for finance lease liabilities	$ 16,452	$ 23,027