The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 10

-Paragraph c

-Subparagraph 4(ii)

-Article 4

Name:	us-gaap_UnamortizedCostsCapitalizedLessRelatedDeferredIncomeTaxesExceedCeilingLimitationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Property, Pland and Equipment - Additional Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Property, Plant and Equipment
Cumulative full cost ceiling limitation impairment	$ 3,700,000,000		$ 3,500,000,000
Impairment	164,779,000	0
Repsol E&P USA, Inc.
Property, Plant and Equipment
Drilling carry received or billed	72,300,000
Atinum MidCon I, LLC and Repsol E&P USA, Inc.
Property, Plant and Equipment
Drilling carry received or billed		$ 123,300,000