CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net (loss) income	$ 100,739	$ (39,873)	$ 44,102
Adjustments to reconcile net income (loss) to net cash from operating activities:
Depreciation and amortization	288,422	287,002	274,194
Goodwill impairment charges	0	34,013	31,992
Allowance for doubtful accounts	7,901	6,907	4,793
Amortization of deferred financing costs and debt discount	3,482	3,537	3,280
Accretion of environmental liabilities	9,460	10,177	10,402
Changes in environmental liability estimates	(195)	(4,254)	(11,345)
Deferred income taxes	(83,335)	15,184	1,930
Other expense (income), net	6,119	(5,685)	1,380
Stock-based compensation	13,146	10,481	8,550
Excess tax benefit of stock-based compensation	0	(1,198)	(71)
Net tax benefit (deficiency) on stock-based awards	0	1,165	(82)
Gain on sale of businesses	(30,732)	(16,884)	0
Loss on early extinguishment of debt	7,891	0	0
Environmental expenditures	(12,965)	(12,170)	(20,130)
Changes in assets and liabilities, net of acquisitions:
Accounts receivable and unbilled accounts receivable	(33,764)	(15,009)	55,271
Inventories and supplies	(5,002)	(16,080)	14,059
Other current assets	16,720	(8,036)	48,760
Accounts payable	(10,684)	(3,503)	(16,299)
Other current and long-term liabilities	8,495	13,850	(54,403)
Net cash from operating activities	285,698	259,624	396,383
Cash flows used in investing activities:
Additions to property, plant and equipment	(167,007)	(219,384)	(257,196)
Proceeds from sale and disposal of fixed assets	7,124	20,817	6,195
Acquisitions, net of cash acquired	(49,227)	(206,915)	(94,345)
Additions to intangible assets including costs to obtain or renew permits	(1,617)	(2,831)	(5,296)
Purchases of available-for-sale securities	(38,342)	(598)	0
Proceeds on sale of businesses, net of transactional costs	45,426	47,134	0
Proceeds from sale of long-term investments	376	0	0
Net cash used in investing activities	(203,267)	(361,777)	(350,642)
Cash flows (used in) from financing activities:
Change in uncashed checks	(5,940)	(3,177)	(14,630)
Proceeds from exercise of stock options	46	627	397
Tax payments related to withholdings on vested restricted stock	(3,149)	(2,819)	(2,159)
Repurchases of common stock	(48,971)	(22,188)	(73,347)
Excess tax benefit of stock-based compensation	0	1,198	71
Deferred financing costs paid	(5,718)	(4,031)	0
Payments on capital leases	0	0	(511)
Premiums paid on early extinguishment of debt	(6,028)	0	0
Principal payment on debt	(402,000)	0	0
Issuance of senior secured notes, net of discount	399,000	0	0
Issuance of senior unsecured notes, including premium	0	250,625	0
Net cash (used in) from financing activities	(72,760)	220,235	(90,179)
Effect of exchange rate change on cash	2,731	4,207	(17,733)
Increase (decrease) in cash and cash equivalents	12,402	122,289	(62,171)
Cash and cash equivalents, beginning of year	306,997	184,708	246,879
Cash and cash equivalents, end of year	319,399	306,997	184,708
Cash payments for interest and income taxes:
Interest paid	93,174	88,669	73,926
Income taxes paid	18,682	29,255	52,970
Non-cash investing activities:
Property, plant and equipment accrued	16,109	9,214	32,677
Transfer of inventory to property, plant and equipment	12,641	0	0
Receivable for estimated purchase price adjustment	$ 0	$ 1,910	$ 1,000