Statements of Condensed Consolidated Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 203,399	$ 103,481
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	63,252	53,057
Depreciation, depletion, and amortization	317,693	223,206
Provision for losses on accounts receivable	2,246	(2,638)
Other income	(4,441)	(11,040)
Stock-based compensation expense	27,480	17,235
Unrealized losses (gains) on derivatives and inventory	4,756	1,118
Lease impairment	8,133	1,095
Noncash financial instrument put premiums		8,227
Changes in other assets and liabilities:
Dividend from Nora Gathering, LLC	4,500	7,750
Accounts receivable and unbilled revenues	(11,093)	72,790
Inventory	23,952	51,004
Accounts payable	(18,005)	(54,274)
Other items, net	(13,046)	(52,572)
Net cash provided by operating activities	608,826	418,439
Cash flows from investing activities:
Capital expenditures	(805,019)	(662,320)
Proceeds from sale of assets		3,746
Net cash used in investing activities	(805,019)	(658,574)
Cash flows from financing activities:
Increase in short-term loans	55,000
Dividends paid	(9,038)	(65,887)
Distributions to noncontrolling interests	(10,350)
Repayments and retirements of long-term debt	(20,161)	(9,532)
Proceeds and tax benefits from exercises under employee compensation plans	15,387	1,499
Revolving credit facility origination fees		(2,158)
Net cash provided by (used in) financing activities	30,838	(76,078)
Net change in cash and cash equivalents	(165,355)	(316,213)
Cash and cash equivalents at beginning of period	182,055	831,251
Cash and cash equivalents at end of period	16,700	515,038
Cash paid during the period for:
Interest, net of amount capitalized	75,281	81,529
Income taxes, net	$ 25,061	$ 13,193