CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Cash and cash equivalents	$ 120	$ 282,248
Accounts receivable (Note 2)	322,630us-gaap_AccountsReceivableNetCurrent	318,371us-gaap_AccountsReceivableNetCurrent
Derivative asset	402,668us-gaap_DerivativeAssetsCurrent	21,559us-gaap_DerivativeAssetsCurrent
Deferred income taxes	0us-gaap_DeferredTaxAssetsNetCurrent	10,749us-gaap_DeferredTaxAssetsNetCurrent
Prepaid expenses and other	19,625	14,574
Total current assets	745,043us-gaap_AssetsCurrent	647,501us-gaap_AssetsCurrent
Proved oil and gas properties	7,348,436	5,637,462
Less - accumulated depletion, depreciation, and amortization	(3,233,012)	(2,583,698)
Unproved oil and gas properties	532,498	271,100
Wells in progress	503,734us-gaap_WellsInProcessOfDrilling	279,654us-gaap_WellsInProcessOfDrilling
Oil and gas properties held for sale, net of accumulated depletion, depreciation and amortization of $22,482 and $7,390, respectively	17,891	19,072
Other property and equipment, net of accumulated depreciation of $37,079 and $28,775, respectively	334,356	236,202
Total property and equipment, net	5,503,903us-gaap_PropertyPlantAndEquipmentNet	3,859,792us-gaap_PropertyPlantAndEquipmentNet
Derivative asset	189,540us-gaap_DerivativeAssetsNoncurrent	30,951us-gaap_DerivativeAssetsNoncurrent
Restricted cash	0	96,713
Other noncurrent assets	78,214us-gaap_OtherAssetsNoncurrent	70,208us-gaap_OtherAssetsNoncurrent
Total other noncurrent assets	267,754us-gaap_AssetsNoncurrent	197,872us-gaap_AssetsNoncurrent
Total Assets	6,516,700us-gaap_Assets	4,705,165us-gaap_Assets
LIABILITIES
Accounts payable and accrued expenses (note 2)	640,684	606,751
Derivative liability	0us-gaap_DerivativeLiabilitiesCurrent	26,380us-gaap_DerivativeLiabilitiesCurrent
Deferred tax liability	142,976us-gaap_DeferredTaxLiabilitiesCurrent	0us-gaap_DeferredTaxLiabilitiesCurrent
Other current liabilities	1,000us-gaap_OtherLiabilitiesCurrent	6,000us-gaap_OtherLiabilitiesCurrent
Total current liabilities	784,660us-gaap_LiabilitiesCurrent	639,131us-gaap_LiabilitiesCurrent
Revolving credit facility	166,000us-gaap_LineOfCredit	0us-gaap_LineOfCredit
Senior Notes (note 5)	2,200,000us-gaap_SeniorNotes	1,600,000us-gaap_SeniorNotes
Asset retirement obligation	120,867	118,692
Net Profits Plan liability	27,136	56,985
Deferred income taxes; Net, non-current	891,681	650,125
Derivative liability	70us-gaap_DerivativeLiabilitiesNoncurrent	4,640us-gaap_DerivativeLiabilitiesNoncurrent
Other noncurrent liabilities	39,631us-gaap_OtherLiabilitiesNoncurrent	28,771us-gaap_OtherLiabilitiesNoncurrent
Total noncurrent liabilities	3,445,385us-gaap_LiabilitiesNoncurrent	2,459,213us-gaap_LiabilitiesNoncurrent
Commitments and contingencies (note 6)
STOCKHOLDERS' EQUITY
Common stock, $0.01 par value - authorized: 200,000,000 shares; issued: 67,463,060 and 67,078,853 shares outstanding, respectively; net of treasury shares: 67,463,060 and 67,056,441, respectively	675us-gaap_CommonStockValue	671us-gaap_CommonStockValue
Additional paid-in capital	283,295	257,720
Treasury stock, at cost: zero and 22,412, respectively	0us-gaap_TreasuryStockValue	(823)us-gaap_TreasuryStockValue
Retained earnings	2,013,997	1,354,669
Accumulated other comprehensive loss	(11,312)	(5,416)
Total stockholders' equity	2,286,655	1,606,821
Total Liabilities and Stockholders' Equity	$ 6,516,700	$ 4,705,165

Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant