UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income	$ 37,220	$ 18,116
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	149,572	147,604
Allowance for doubtful accounts	(2,233)	7,389
Amortization of deferred financing costs and debt discount	2,000	1,881
Accretion of environmental liabilities	5,134	4,878
Changes in environmental liability estimates	(748)	(673)
Deferred income taxes	(1,636)	(10)
Other income, net	(2,419)	(547)
Stock-based compensation	9,643	6,639
Environmental expenditures	(6,134)	(4,585)
Changes in assets and liabilities, net of acquisitions
Accounts receivable and unbilled accounts receivable	(13,284)	(62,764)
Inventories and supplies	(4,129)	(18,625)
Other current and non-current assets	(10,706)	180
Accounts payable	(20,915)	23,605
Other current and long-term liabilities	(2,895)	6,582
Net cash from operating activities	138,470	129,670
Cash flows used in investing activities:
Additions to property, plant and equipment	(118,372)	(94,139)
Proceeds from sale and disposal of fixed assets	7,389	2,641
Acquisitions, net of cash acquired	(29,479)	(123,750)
Additions to intangible assets including costs to obtain or renew permits	(1,923)	(2,106)
Proceeds from sale of available-for-sale securities	26,518	11,214
Purchases of available-for-sale securities	(24,001)	(10,001)
Net cash used in investing activities	(139,868)	(216,141)
Inventories and supplies
Change in uncashed checks	(3,514)	(2,803)
Tax payments related to withholdings on vested restricted stock	(4,980)	(2,175)
Repurchases of common stock	(11,272)	(26,482)
Deferred financing costs paid	0	(468)
Payments on finance lease	(259)	0
Principal payments on debt	(3,768)	(2,000)
Net cash used in financing activities	(23,793)	(33,928)
Effect of exchange rate change on cash	3,139	(1,932)
Decrease in cash and cash equivalents	(22,052)	(122,331)
Cash and cash equivalents, beginning of period	226,507	319,399
Cash and cash equivalents, end of period	204,455	197,068
Cash payments for interest and income taxes:
Interest paid	39,369	40,745
Income taxes paid	12,697	14,118
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	27,773
Operating cash flows from finance lease	612
Financing cash flows from finance lease	259	0
Non-cash investing activities:
Property, plant and equipment accrued	14,103	$ 13,041
ROU assets obtained in exchange for new operating lease liabilities	5,575
ROU asset obtained in exchange for new finance lease liability	$ 23,027