CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
OPERATING ACTIVITIES
Net income	$ 102,671	$ 75,492
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and other non-cash charges	113,308	107,056
Stock-based compensation expense	4,717	4,251
Loss on disposition of assets, net	3,637	4,397
Deferred income tax benefit	(23,255)	(15,635)
Excess tax benefits for share-based payments	(4,416)	(3,197)
(Increase) decrease in assets:
Accounts receivable	(128,862)	6,416
Income taxes receivable	(6,738)	7,431
Inventories	(12,261)	6,276
Prepaid expenses	3,049	2,706
Other current assets	(3,342)	(964)
Other non-current assets	(467)	26
Increase (decrease) in liabilities:
Accounts payable	33,231	7,090
Income taxes payable	535	3,683
Accrued payroll and related expenses	1,048	(3,253)
Accrued insurance expenses	552	169
Accrued state, local and other taxes	3,409	606
Other accrued expenses	139	(1,586)
Pension liabilities	1,167	915
Long-term accrued insurance expenses	1,187	605
Other long-term liabilities	2,179	(1,836)
Net cash provided by operating activities	91,488	200,648
INVESTING ACTIVITIES
Capital expenditures	(112,804)	(108,490)
Proceeds from sale of assets	11,958	5,158
Net cash used for investing activities	(100,846)	(103,332)
FINANCING ACTIVITIES
Payment of dividends	(45,883)	(44,030)
Borrowings from notes payable to banks	537,400	350,500
Repayments of notes payable to banks	(459,300)	(390,300)
Debt issue costs for notes payable to banks	(667)
Excess tax benefits for share-based payments	4,416	3,197
Cash paid for common stock purchased and retired	(13,144)	(20,587)
Net cash provided by (used for) financing activities	22,822	(101,220)
Net increase (decrease) in cash and cash equivalents	13,464	(3,904)
Cash and cash equivalents at beginning of period	8,700	14,163
Cash and cash equivalents at end of period	22,164	10,259
Supplemental cash flows disclosure:
Interest paid, net of amounts capitalized	443	406
Income taxes paid, net	93,108	53,298
Supplemental disclosure of noncash investing activities:
Capital expenditures included in accounts payable	$ 18,205	$ 15,793