CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
OPERATING ACTIVITIES
Net income	$ 75,492	$ 153,015
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and other non-cash charges	107,056	105,121
Stock-based compensation expense	4,251	3,902
Loss on disposition of assets, net	4,397	3,308
Deferred income tax (benefit) provision	(15,635)	6,931
Excess tax benefits for share-based payments	(3,197)	(2,172)
(Increase) decrease in assets:
Accounts receivable	6,416	47,766
Income taxes receivable	7,431	12,449
Inventories	6,276	(18,621)
Prepaid expenses	2,706	2,478
Other current assets	(964)	(6,864)
Other non-current assets	26	(3,661)
Increase (decrease) in liabilities:
Accounts payable	7,090	8,399
Income taxes payable	3,683	(7,840)
Accrued payroll and related expenses	(3,253)	(1,524)
Accrued insurance expenses	169	(281)
Accrued state, local and other taxes	606	3,368
Other accrued expenses	(1,586)	(1,056)
Pension liabilities	915	(2,148)
Long-term accrued insurance expenses	605	230
Other long-term liabilities	(1,836)	(666)
Net cash provided by operating activities	200,648	302,134
INVESTING ACTIVITIES
Capital expenditures	(108,490)	(204,202)
Proceeds from sale of assets	5,158	7,999
Net cash used for investing activities	(103,332)	(196,203)
FINANCING ACTIVITIES
Payment of dividends	(44,030)	(35,083)
Borrowings from notes payable to banks	350,500	450,850
Repayments of notes payable to banks	(390,300)	(492,150)
Excess tax benefits for share-based payments	3,197	2,172
Cash paid for common stock purchased and retired	(20,587)	(30,024)
Proceeds received upon exercise of stock options		167
Net cash used for financing activities	(101,220)	(104,068)
Net (decrease) increase in cash and cash equivalents	(3,904)	1,863
Cash and cash equivalents at beginning of period	14,163	7,393
Cash and cash equivalents at end of period	10,259	9,256
Supplemental cash flows disclosure:
Interest paid, net of amounts capitalized	406	978
Income taxes paid, net	53,298	84,965
Supplemental disclosure of noncash investing activities:
Capital expenditures included in accounts payable	$ 15,793	$ 18,272