CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
OPERATING ACTIVITIES
Net income	$ 274,436	$ 296,381	$ 146,742
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and other non-cash charges	214,153	179,787	133,253
Stock-based compensation expense	7,860	8,075	4,909
Loss (gain) on disposition of assets, net	6,099	3,831	(3,758)
Deferred income tax provision	4,821	77,074	22,262
Excess tax benefits for share-based payments	(2,724)	(3,371)	(651)
Changes in current assets and liabilities:
Accounts receivable	73,809	(167,312)	(163,162)
Income taxes receivable	9,295	9,817	1,584
Inventories	(40,354)	(36,511)	(8,130)
Prepaid expenses	(2,284)	(2,783)	(1,041)
Other current assets	26,189	(30,524)	189
Accounts payable	(4,929)	30,102	14,191
Income taxes payable	(4,277)	4,917	5,141
Accrued payroll and related expenses	(1,627)	9,799	13,173
Accrued insurance expenses	408	603	826
Accrued state, local and other taxes	2,260	2,078	987
Other accrued expenses	1,412	958	112
Changes in working capital	59,902	(178,856)	(136,130)
Changes in other assets and liabilities:
Pension liabilities	(589)	1,249	1,628
Accrued insurance expenses	1,400	511	(108)
Other non-current assets	(6,415)	294	(920)
Other non-current liabilities	990	1,032	1,430
Net cash provided by operating activities	559,933	386,007	168,657
INVESTING ACTIVITIES
Capital expenditures	(328,936)	(416,400)	(187,486)
Increased ownership interest in subsidiary	(6,211)
Proceeds from sale of assets	19,309	24,763	15,717
Net cash used for investing activities	(315,838)	(391,637)	(171,769)
FINANCING ACTIVITIES
Payment of dividends	(114,069)	(47,327)	(20,647)
Borrowings from notes payable to banks	844,050	940,850	516,600
Repayments of notes payable to banks	(940,350)	(858,800)	(485,650)
Debt issue costs for notes payable to banks		(415)	(1,886)
Excess tax benefits for share-based payments	2,724	3,371	651
Cash paid for common stock purchased and retired	(30,224)	(34,419)	(1,650)
Proceeds received upon exercise of stock options	544	728	240
Net cash (used for) provided by financing activities	(237,325)	3,988	7,658
Net increase (decrease) in cash and cash equivalents	6,770	(1,642)	4,546
Cash and cash equivalents at beginning of year	7,393	9,035	4,489
Cash and cash equivalents at end of year	$ 14,163	$ 7,393	$ 9,035