Statements of Condensed Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:
Net income	$ 109,281	$ 72,035
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	34,347	39,363
Depreciation, depletion and amortization	149,116	107,525
Provision for losses on accounts receivable	1,962	196
Other income	(2,330)	(5,791)
Stock-based compensation expense	10,334	8,256
Unrealized (gains) losses on derivatives and inventory	(1,326)	5,484
Lease impairment	2,980	692
Changes in other assets and liabilities:
Accounts receivable and unbilled revenues	(8,825)	36,251
Inventory	37,789	55,628
Accounts payable	(18,025)	(55,969)
Other items, net	(10,063)	(41,546)
Net cash provided by operating activities	305,240	222,124
Cash flows from investing activities:
Capital expenditures	(304,257)	(269,587)
Proceeds from sale of assets		2,391
Net cash used in investing activities	(304,257)	(267,196)
Cash flows from financing activities:
Dividends paid	(4,516)	(32,938)
Distributions to noncontrolling interests	(5,031)
Repayments and retirements of long-term debt	(20,161)	(9,532)
Proceeds and tax benefits from exercises under employee compensation plans	6,995	1,499
Net cash used in financing activities	(22,713)	(40,971)
Net change in cash and cash equivalents	(21,730)	(86,043)
Cash and cash equivalents at beginning of period	182,055	831,251
Cash and cash equivalents at end of period	160,325	745,208
Cash paid during the period for:
Interest, net of amount capitalized	10,446	13,044
Income taxes, net	$ 3,661	$ 2,214