UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income	$ 73,589	$ 49,205
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	223,328	220,686
Allowance for doubtful accounts	(745)	6,869
Amortization of deferred financing costs and debt discount	2,908	2,841
Accretion of environmental liabilities	7,624	7,328
Changes in environmental liability estimates	(585)	(301)
Deferred income taxes	(973)	61
Other (income) expense, net	(1,992)	449
Stock-based compensation	14,664	10,726
Loss on early extinguishment of debt	6,119	2,469
Environmental expenditures	(12,804)	(7,238)
Changes in assets and liabilities, net of acquisitions
Accounts receivable and unbilled accounts receivable	(31,408)	(76,249)
Inventories and supplies	(11,982)	(20,534)
Other current and non-current assets	(5,425)	(523)
Accounts payable	3,035	22,041
Other current and long-term liabilities	19,322	29,385
Net cash from operating activities	284,675	247,215
Cash flows used in investing activities:
Additions to property, plant and equipment	(174,533)	(150,722)
Proceeds from sale and disposal of fixed assets	8,948	6,111
Acquisitions, net of cash acquired	(29,479)	(151,023)
Additions to intangible assets including costs to obtain or renew permits	(2,896)	(3,500)
Proceeds from sale of available-for-sale securities	41,612	20,123
Purchases of available-for-sale securities	(30,761)	(20,471)
Net cash used in investing activities	(187,109)	(299,482)
Cash flows used in financing activities:
Change in uncashed checks	(3,516)	(3,476)
Tax payments related to withholdings on vested restricted stock	(5,505)	(2,566)
Repurchases of common stock	(16,390)	(33,581)
Deferred financing costs paid	(10,053)	(3,938)
Premiums paid on early extinguishment of debt	(2,689)	(1,219)
Payments on finance lease	(327)	0
Principal payments on debt	(850,652)	(403,884)
Issuance of unsecured senior notes	845,000	0
Issuance of secured senior notes, net of discount	0	348,250
Borrowing from revolving credit facility	0	50,000
Net cash used in financing activities	(44,132)	(50,414)
Effect of exchange rate change on cash	2,292	(1,221)
Increase (decrease) in cash and cash equivalents	55,726	(103,902)
Cash and cash equivalents, beginning of period	226,507	319,399
Cash and cash equivalents, end of period	282,233	215,497
Cash payments for interest and income taxes:
Interest paid	52,440	58,312
Income taxes paid	23,797	16,071
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	42,105	0
Operating cash flows from finance lease	979	0
Financing cash flows from finance lease	327	0
Non-cash investing activities:
Property, plant and equipment accrued	14,875	13,834
ROU assets obtained in exchange for new operating lease liabilities	8,008	0
ROU assets obtained in exchange for new finance lease liabilities	$ 31,011	$ 0