Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income (Loss)	$ 172,226	$ 263,869
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depletion of Oil and Gas Properties	152,978	108,120
Deferred Income Tax Expense (Benefit)	97,128	147,916
Unrealized Gain (Loss) on Derivatives	26,879	(158,932)
Excess Tax Benefit from Share-based Compensation, Operating Activities	(6,552)	(16,420)
Share-based Compensation	6,446	6,137
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities, Other	521	271
Increase (Decrease) in Operating Capital [Abstract]
Increase (Decrease) in Restricted Cash for Operating Activities	0	(82)
Increase (Decrease) in Accounts Receivable	(12,336)	(23,763)
Increase (Decrease) in Prepaid, Deferred Expense and Other Assets	(1,571)	(3,911)
Increase (Decrease) in Other Operating Assets	7	2,905
Increase (Decrease) in Accounts Payable and Accrued Liabilities	38,129	37,891
Other long-term obligations	327	8,181
Increase (Decrease) in Accrued Income Taxes Payable	3,198	0
Net Cash Provided by (Used in) Operating Activities	477,380	372,182
Net Cash Provided by (Used in) Investing Activities [Abstract]
Acquisition Costs	0	(332,970)
Oil and gas property expenditures	(695,810)	(539,783)
Gathering system expenditures	(21,417)	(32,979)
Restricted Cash Non Current	0	28,257
Change in capital cost accrual	27,158	48,324
Proceeds from Sale of Productive Assets	0	68,420
Inventory	(123)	1,006
Payments to Acquire Productive Assets	(489)	(342)
Net Cash Provided by (Used in) Investing Activities	(690,681)	(760,067)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from Issuance of Long-term Debt	504,000	583,000
Repayments of Long-term Debt	(350,000)	(697,000)
Proceeds from issuance of Senior Notes	0	500,000
Payments of Financing Costs	0	(2,265)
Payments for Repurchase of Equity	(20,629)	(23,707)
Excess Tax Benefit from Share-based Compensation, Financing Activities	6,552	16,420
Proceeds from Stock Options Exercised	9,242	5,512
Net Cash Provided by (Used in) Financing Activities	149,165	381,960
Cash and Cash Equivalents, Period Increase (Decrease)	(64,136)	(5,925)
Cash and Cash Equivalents, at Carrying Value	70,834	14,254
Cash and Cash Equivalents, at Carrying Value	$ 6,698	$ 8,329

The net change in the reporting period in the amounts capitalized associated with the development costs incurred to provide facilities for gathering condensate and natural gas.

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The net change in the reporting period of liabilities incurred and payable to vendors associated with accrued capital expenditures for oil and gas drilling.

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The net change in the reporting period of inventories less all valuation and other allowances.

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The net change in the reporting period in amounts due for noncurrent obligations not separately disclosed in the balance sheet due to materiality considerations.

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The net change in the reporting period in amounts capitalized in oil and gas properties associated with exploration and development costs incurred to obtain access to proved and unproved reserves and to provide facilities for extracting, treating and storing oil and natural gas.

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The cash inflow from borrowing associated with the Senior Notes

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The net cash outflow for funds held in escrow and are associated with underlying transactions that are classified as investing activities.

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The capitalized costs incurred to purchase, lease or otherwise acquire a property, including costs of lease bonuses and options to purchase or lease properties, the portion of costs applicable to minerals when land including mineral rights is purchased in fee, brokers' fees, recording fees, legal costs, and other costs incurred in acquiring properties.

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Transactions that do not result in cash inflows or outflows in the period in which they occur, but affect net income and thus are removed when calculating net cash flow from operating activities using the indirect cash flow method. This element is used when there is not a more specific and appropriate element.

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Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits should not be reported as cash and cash equivalents.

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The net change between the beginning and ending balance of cash and cash equivalents.

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The component of income tax expense for the period representing the net change in the entity's deferred tax assets and liabilities pertaining to continuing operations.

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The noncash expense charged against earnings to recognize the consumption of oil and gas reserves that are part of an entities' assets.

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Reductions in the entity's income taxes that arise when compensation cost (from non-qualified share-based compensation) recognized on the entity's tax return exceeds compensation cost from share-based compensation recognized in financial statements. This element represents the cash inflow reported in the enterprise's financing activities.

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The net change during the reporting period in the aggregate amount of obligations and expenses incurred but not paid.

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The net change during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services.

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The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the reporting entity's earnings.

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The net change during the reporting period in other operating assets not otherwise defined in the taxonomy.

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The net change during the reporting period in the value of this group of assets within the working capital section.

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The net cash inflow (outflow) for the net change associated with funds that are not available for withdrawal or use (such as funds held in escrow) and are associated with underlying transactions that are classified as operating activities. This may include cash restricted for regulatory purposes.

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The net cash inflow (outflow) from financing activity for the period.

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The net cash inflow (outflow) from investing activity.

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The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities generally involve producing and delivering goods and providing services. Operating activity cash flows include transactions, adjustments, and changes in value that are not defined as investing or financing activities.

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The net cash from (used in) all of the entity's operating activities, including those of discontinued operations, of the reporting entity. Operating activities include all transactions and events that are not defined as investing or financing activities. Operating activities generally involve producing and delivering goods and providing services. Cash flows from operating activities are generally the cash effects of transactions and other events that enter into the determination of net income.

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The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.

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The cash outflow to reacquire common and preferred stock.

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The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

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The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

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The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

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The cash inflow from the sale of property, plant and equipment (capital expenditures), software, and other intangible assets.

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The cash inflow associated with the amount received from holders exercising their stock options.

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The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock options, amortization of restricted stock, and adjustment for officers compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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The increases (decreases) in the market value of derivative instruments, including options, swaps, futures, and forward contracts, which were included in earnings in the period.

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