UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 18,116	$ 4,487
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	147,604	143,943
Allowance for doubtful accounts	7,389	3,580
Amortization of deferred financing costs and debt discount	1,881	1,660
Accretion of environmental liabilities	4,878	4,706
Changes in environmental liability estimates	(673)	(129)
Deferred income taxes	(10)	190
Stock-based compensation	6,639	5,172
Other (income) expense, net	(547)	2,382
Gain on sale of business	0	(31,722)
Loss on early extinguishment of debt	0	6,045
Environmental expenditures	(4,585)	(6,102)
Changes in assets and liabilities, net of acquisitions
Accounts receivable and unbilled accounts receivable	(62,764)	(31,154)
Inventories and supplies	(18,625)	(6,307)
Other current assets	180	13,918
Accounts payable	23,605	(2,686)
Other current and long-term liabilities	6,582	8,948
Net cash from operating activities	129,670	116,931
Cash flows used in investing activities:
Additions to property, plant and equipment	(94,139)	(88,742)
Proceeds from sale and disposal of fixed assets	2,641	2,121
Acquisitions, net of cash acquired	(123,750)	(9,277)
Proceeds from sale of businesses, net of transactional costs	0	46,391
Additions to intangible assets, including costs to obtain or renew permits	(2,106)	(1,239)
Proceeds from sale of available-for-sale securities	11,214	376
Purchases of available-for-sale securities	(10,001)	0
Net cash used in investing activities	(216,141)	(50,370)
Cash flows (used in) from financing activities:
Change in uncashed checks	(2,803)	(8,361)
Proceeds from exercise of stock options	0	46
Tax payments related to withholdings on vested restricted stock	(2,175)	(2,132)
Repurchases of common stock	(26,482)	(12,257)
Deferred financing costs paid	(468)	(4,727)
Premiums paid on early extinguishment of debt	0	(4,665)
Principal payment on debt	(2,000)	(296,202)
Issuance of senior secured notes, net of discount	0	399,000
Net cash (used in) from financing activities	(33,928)	70,702
Effect of exchange rate change on cash	(1,932)	2,106
(Decrease) increase in cash and cash equivalents	(122,331)	139,369
Cash and cash equivalents, beginning of period	319,399	306,997
Cash and cash equivalents, end of period	197,068	446,366
Cash payments for interest and income taxes:
Interest paid	40,745	50,432
Income taxes paid	14,118	13,407
Non-cash investing activities:
Property, plant and equipment accrued	13,041	16,213
Transfer of inventory to property, plant and equipment	$ 0	$ 12,641