XML 15 R54.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Hedging Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 financial_institution | Sep. 30, 2013 | Dec. 31, 2013 financial_institution
General Discussion of Derivative Instruments and Hedging Activities [Abstract] |  |  |  |  |
Number of financial institutions |  |  | 4 |  | 4
Gain on fair value hedge ineffectiveness, net | $ 29.5 | $ (6.7) | $ 23.0 | $ (1.3) |

X
- Definition Number Of Financial Institutions + References No definition available. + Details
Name: | gpor_NumberOfFinancialInstitutions
Namespace Prefix: | gpor_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of gain (loss)recognized in the income statement from the hedging ineffectiveness of a fair value hedge. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 + Details
Name: | us-gaap_GainLossOnFairValueHedgeIneffectivenessNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_GeneralDiscussionOfDerivativeInstrumentsAndHedgingActivitiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration