CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income (loss)	$ 65,636	$ 100,739	$ (39,873)
Adjustments to reconcile net income (loss) to net cash from operating activities:
Depreciation and amortization	298,625	288,422	287,002
Goodwill impairment charge	0	0	34,013
Allowance for doubtful accounts	15,817	7,901	6,907
Amortization of deferred financing costs and debt discount	3,846	3,482	3,537
Accretion of environmental liabilities	9,806	9,460	10,177
Changes in environmental liability estimates	2,147	(195)	(4,254)
Deferred income taxes	19,089	(83,335)	15,184
Other expense (income), net	4,510	6,119	(5,685)
Stock-based compensation	16,792	13,146	10,481
Excess tax benefit of stock-based compensation	0	0	(1,198)
Net tax benefit on stock-based awards	0	0	1,165
Gain on sale of businesses	0	(30,732)	(16,884)
Loss on early extinguishment of debt	2,488	7,891	0
Environmental expenditures	(10,115)	(12,965)	(12,170)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(79,563)	(33,764)	(15,009)
Inventories and supplies	(26,958)	(5,002)	(16,080)
Other current assets	(7,946)	16,720	(8,036)
Accounts payable	46,915	(10,684)	(3,503)
Other current and long-term liabilities	12,121	8,495	13,850
Net cash from operating activities	373,210	285,698	259,624
Cash flows used in investing activities:
Additions to property, plant and equipment	(193,344)	(167,007)	(219,384)
Proceeds from sale and disposal of fixed assets	15,445	7,124	20,817
Acquisitions, net of cash acquired	(151,023)	(49,227)	(206,915)
Additions to intangible assets including costs to obtain or renew permits	(4,688)	(1,617)	(2,831)
Purchases of available-for-sale securities	(44,772)	(38,342)	(598)
Proceeds from sale of available-for-sale securities	28,723	376	0
Proceeds from sale of businesses, net of transactional costs	0	45,426	47,134
Net cash used in investing activities	(349,659)	(203,267)	(361,777)
Cash flows (used in) from financing activities:
Change in uncashed checks	132	(5,940)	(3,177)
Proceeds from exercise of stock options	0	46	627
Tax payments related to withholdings on vested restricted stock	(3,266)	(3,149)	(2,819)
Repurchases of common stock	(45,080)	(48,971)	(22,188)
Excess tax benefit of stock-based compensation	0	0	1,198
Deferred financing costs paid	(4,027)	(5,718)	(4,031)
Premiums paid on early extinguishment of debt	(1,238)	(6,028)	0
Principal payments on debt	(405,768)	(402,000)	0
Issuance of senior secured notes, net of discount	348,250	399,000	0
Issuance of senior secured notes, net of discount	0	0	250,625
Borrowing from revolving credit facility	50,000	0	0
Payment on revolving credit facility	(50,000)	0	0
Net cash (used in) from financing activities	(110,997)	(72,760)	220,235
Effect of exchange rate change on cash	(5,446)	2,731	4,207
(Decrease) increase in cash and cash equivalents	(92,892)	12,402	122,289
Cash and cash equivalents, beginning of year	319,399	306,997	184,708
Cash and cash equivalents, end of year	226,507	319,399	306,997
Cash payments for interest and income taxes:
Interest paid	89,171	93,174	88,669
Income taxes paid	20,036	18,682	29,255
Non-cash investing activities:
Property, plant and equipment accrued	15,657	16,109	9,214
Transfer of inventory to property, plant and equipment	0	12,641	0
(Payable) receivable for estimated purchase price adjustment	$ (4,032)	$ 0	$ 1,910