Condensed Consolidating Financial Information - Schedule of Condensed Consolidating Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
ASSETS
Cash and cash equivalents	$ 10,188	$ 45,811	$ 56,298	$ 91,901
Accounts receivable	243,169	306,471
Prepaid expenses	16,954us-gaap_PrepaidExpenseCurrent	14,273us-gaap_PrepaidExpenseCurrent
Other current assets	293,230	330,052
Oil and gas properties (successful efforts method)	6,187,638	5,966,140
Other property and equipment	356,940us-gaap_PropertyPlantAndEquipmentOther	313,439us-gaap_PropertyPlantAndEquipmentOther
Less: accumulated depreciation, depletion, amortization and impairment	(1,215,216)	(1,092,793)
Other long-term assets	40,988	55,019
Total assets	5,916,937us-gaap_Assets	5,938,412us-gaap_Assets
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accounts payable	9,339us-gaap_AccountsPayableCurrent	20,958us-gaap_AccountsPayableCurrent
Other current liabilities	632,900us-gaap_OtherLiabilitiesCurrent	774,170us-gaap_OtherLiabilitiesCurrent
Long-term debt	2,365,000us-gaap_LongTermDebtNoncurrent	2,700,000us-gaap_LongTermDebtNoncurrent
Other long-term liabilities	585,453	570,983
Common stock	1,372us-gaap_CommonStockValue	1,001us-gaap_CommonStockValue
Other equity	2,322,873oas_StockholdersEquityOtherEquity
Equity	2,324,245us-gaap_StockholdersEquity	1,872,301us-gaap_StockholdersEquity
Total liabilities and stockholders’ equity	5,916,937	5,938,412
Parent/Issuer [Member]
ASSETS
Cash and cash equivalents	774	776	936	34,277
Accounts receivable – affiliates	1,032	781
Prepaid expenses		297
Other current assets	148
Investments in and advances to subsidiaries	4,499,571	4,032,494
Other long-term assets	190,812	178,752
Total assets	4,692,337	4,213,100
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accounts payable – affiliates	143,517	91,459
Other current liabilities	24,575	49,340
Long-term debt	2,200,000	2,200,000
Common stock	1,372
Other equity	2,322,873
Equity		1,872,301
Total liabilities and stockholders’ equity	4,692,337	4,213,100
Combined Guarantor Subsidiaries [Member]
ASSETS
Cash and cash equivalents	9,414	45,035	55,362	57,624
Accounts receivable	243,169	306,471
Accounts receivable – affiliates	143,517	91,459
Prepaid expenses		13,976
Other current assets	293,082	330,052
Oil and gas properties (successful efforts method)	6,187,638	5,966,140
Other property and equipment	356,940	313,439
Less: accumulated depreciation, depletion, amortization and impairment	(1,215,216)	(1,092,793)
Other long-term assets	12,674	25,584
Total assets	6,031,218	5,999,363
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accounts payable	9,339	20,958
Accounts payable – affiliates	1,032	781
Other current liabilities	608,325	724,830
Long-term debt	165,000	500,000
Other long-term liabilities	747,951	720,300
Other equity	4,499,571
Equity		4,032,494
Total liabilities and stockholders’ equity	6,031,218	5,999,363
Intercompany Eliminations [Member]
ASSETS
Accounts receivable – affiliates	(144,549)	(92,240)
Investments in and advances to subsidiaries	(4,499,571)	(4,032,494)
Other long-term assets	(162,498)	(149,317)
Total assets	(4,806,618)	(4,274,051)
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accounts payable – affiliates	(144,549)	(92,240)
Other long-term liabilities	(162,498)	(149,317)
Other equity	(4,499,571)
Equity		(4,032,494)
Total liabilities and stockholders’ equity	$ (4,806,618)	$ (4,274,051)

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