UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Cash flows from operating activities:
Net income	$ 37,632	$ 33,404
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	135,431	127,474
Pre-tax, non-cash acquisition accounting inventory adjustments	0	13,559
Allowance for doubtful accounts	4,605	3,618
Amortization of deferred financing costs and debt discount	1,576	1,692
Accretion of environmental liabilities	5,333	5,714
Changes in environmental liability estimates	(1,429)	(393)
Deferred income taxes	(1)	(8)
Stock-based compensation	4,340	3,924
Excess tax benefit of stock-based compensation	(644)	(1,326)
Income tax benefit related to stock option exercises	644	1,316
Other expense (income)	(3,523)	(2,180)
Environmental expenditures	(7,443)	(9,793)
Changes in assets and liabilities, net of acquisitions
Accounts receivable	(689)	(20,783)
Inventories and supplies	(9,556)	1,128
Other current assets	(17,574)	5,027
Accounts payable	(46,421)	(33,426)
Other current and long-term liabilities	12,663	8,665
Net cash from operating activities	114,944	137,612
Cash flows from investing activities:
Additions to property, plant and equipment	(138,186)	(141,466)
Proceeds from sales of fixed assets	2,986	2,194
Proceeds from sales of marketable securities	12,947	0
Acquisitions, net of cash acquired	(6,150)	0
Additions to intangible assets, including costs to obtain or renew permits	(2,891)	(2,169)
Net cash used in investing activities	(131,294)	(141,441)
Cash flows from financing activities:
Change in uncashed checks	3,162	40,356
Proceeds from exercise of stock options	0	399
Remittance of shares, net	(2,215)	(169)
Repurchases of common stock	(14,657)	0
Proceeds from employee stock purchase plan	4,364	3,391
Deferred financing costs paid	0	(2,446)
Repayment of long-term obligations	(5,000)	0
Payments on capital leases	(1,190)	(2,588)
Issuance costs related to 2012 issuance of common stock	0	(250)
Excess tax benefit of stock-based compensation	644	1,326
Net cash from financing activities	(14,892)	40,019
Effect of exchange rate change on cash	(187)	(2,548)
(Decrease) increase in cash and cash equivalents	(31,429)	33,642
Cash and cash equivalents, beginning of period	310,073	229,836
Cash and cash equivalents, end of period	278,644	263,478
Cash payments for interest and income taxes:
Interest paid	37,070	36,841
Income taxes paid	14,304	7,275
Non-cash investing and financing activities:
Payable for repurchased shares	1,562	0
Property, plant and equipment accrued	21,934	38,650
Transfer of inventory to property, plant and equipment	$ 0	$ 11,369