CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income (loss)	$ 44,102	$ (28,328)	$ 95,566
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	274,194	276,083	264,449
Goodwill impairment charge	31,992	123,414	0
Pre-tax, non-cash acquisition accounting inventory adjustments	0	0	13,559
Allowance for doubtful accounts	4,793	8,917	7,933
Amortization of deferred financing costs and debt discount	3,280	3,289	3,301
Accretion of environmental liabilities	10,402	10,612	11,541
Changes in environmental liability estimates	(11,345)	(3,367)	(3,682)
Deferred income taxes	1,930	32,320	31,119
Other expense (income)	1,380	(4,380)	(1,705)
Stock-based compensation	8,550	8,800	8,946
Excess tax benefit of stock-based compensation	(71)	(878)	(1,409)
Net tax benefit on stock-based awards	(82)	816	1,399
Environmental expenditures	(20,130)	(20,245)	(19,416)
Changes in assets and liabilities:
Accounts receivable and unbilled accounts receivables	55,271	(14,342)	(54,213)
Inventories and supplies	14,059	(21,339)	(1,144)
Other current assets	48,760	(19,030)	20,857
Accounts payable	(16,299)	(52,026)	37,117
Other current and long-term liabilities	(54,403)	(2,950)	1,621
Net cash from operating activities	396,383	297,366	415,839
Cash flows used in investing activities:
Additions to property, plant and equipment	(257,196)	(257,613)	(280,207)
Proceeds from sales of fixed assets	6,195	8,164	4,699
Acquisitions, net of cash acquired	(94,345)	(16,187)	(63,264)
Additions to intangible assets including costs to obtain or renew permits	(5,296)	(6,519)	(6,740)
Proceeds from sales of investments	0	13,861	0
Other	0	0	0
Net cash used in investing activities	(350,642)	(258,294)	(345,512)
Cash flows (used in) from financing activities:
Change in uncashed checks	(14,630)	15,069	12,268
Proceeds from exercise of stock options	397	0	400
Remittance of shares, net	(2,159)	(2,793)	(731)
Repurchases of common stock	(73,347)	(104,341)	0
Excess tax benefit of stock-based compensation	71	878	1,409
Deferred financing costs paid	0	0	(2,504)
Repayment of long-term obligations	0	(5,000)	0
Proceeds from employee stock purchase plan	0	4,364	7,425
Payments on capital leases	(511)	(2,122)	(4,891)
Issuance costs related to issuances of common stock	0	0	(250)
Net cash (used in) from financing activities	(90,179)	(93,945)	13,126
Effect of exchange rate change on cash	(17,733)	(8,321)	(3,216)
(Decrease) increase in cash and cash equivalents	(62,171)	(63,194)	80,237
Cash and cash equivalents, beginning of year	246,879	310,073	229,836
Cash and cash equivalents, end of year	184,708	246,879	310,073
Cash payments for interest and income taxes:
Interest paid	73,926	75,408	75,627
Income taxes paid (received)	52,970	42,022	(8,162)
Non-cash investing and financing activities:
Property, plant and equipment accrued	32,677	23,563	33,214
Transfer of inventory to property, plant and equipment	0	1,324	11,369
Accrued business combination adjustments	0	355	0
Receivable for estimated purchase price adjustment	$ 1,000	$ 0	$ 0