Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
OPERATING ACTIVITIES:
Net income	$ 40,206	$ 52,439
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, and amortization	77,156	79,047
Unrealized loss on derivatives	6,964	1,993
Deferred tax expense	22,652	33,105
(Gain) loss on disposition of assets	84	(588)
Employee stock compensation plans	4,651	3,692
Other, net	1,601	1,188
Changes in operating assets and liabilities increasing (decreasing) cash:
Accounts receivable	(7,695)	(2,860)
Accounts payable	23,332	(21,735)
Material and supplies	(640)	417
Accrued liabilities	8,937	1,549
Other, net	2,412	(300)
Net cash provided by operating activities	179,660	147,947
INVESTING ACTIVITIES:
Capital expenditures	(192,927)	(192,824)
Producing property and other acquisitions	0	(46)
Proceeds from disposition of assets	1,456	3,451
Net cash used in investing activities	(191,471)	(189,419)
FINANCING ACTIVITIES:
Borrowings under credit agreement	123,300	103,700
Payments under credit agreement	(124,400)	(87,900)
Proceeds from exercise of stock options	72	0
Book overdrafts	13,018	26,032
Net cash provided by financing activities	11,990	41,832
Net increase in cash and cash equivalents	179	360
Cash and cash equivalents, beginning of period	974	835
Cash and cash equivalents, end of period	$ 1,153	$ 1,195