XML 116 R99.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Changes in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items] |  |  |
Sales and transfers of oil and gas produced, net of production costs | $ (1,063,215) | $ (756,257) | $ (312,291)
Net changes in prices, production costs, and development costs | 590,519 | 913,714 | (146,518)
Acquisition of oil and gas reserves in place | 0 | 703,866 | 0
Extensions and discoveries | 519,137 | 618,039 | 186,909
Previously estimated development costs incurred during the period | 402,156 | 390,673 | 176,218
Revisions of previous quantity estimates, less related production costs | (356,933) | 155,200 | (38,448)
Sales of oil and gas reserves in place | (25,882) | 0 | 0
Accretion of discount | 264,356 | 68,804 | 76,433
Net changes in income taxes | (185,157) | (231,545) | (6,495)
Change in production rates and other | 194,180 | 93,030 | (12,099)
Total change in standardized measure of discounted future net cash flows | 339,161 | 1,955,524 | (76,291)
Investment in Grizzly Oil Sands ULC |  |  |
Changes In Standardized Measure of Discontinued Future Net Cash Flows [Line Items] |  |  |
Sales and transfers of oil and gas produced, net of production costs | 0 | 0 | 0
Net changes in prices, production costs, and development costs | 0 | 0 | 0
Acquisition of oil and gas reserves in place | 0 | 0 | 0
Extensions and discoveries | 0 | 0 | 0
Previously estimated development costs incurred during the period | 0 | 0 | 0
Revisions of previous quantity estimates, less related production costs | 0 | 0 | 0
Accretion of discount | 0 | 0 | 0
Net changes in income taxes | 0 | 0 | 0
Change in production rates and other | 0 | 0 | 0
Total change in standardized measure of discounted future net cash flows | $ 0 | $ 0 | $ 0

X
- Definition Change in production rates and other + References No definition available. + Details
Name: | gpor_ChangeInProductionRatesAndOther
Namespace Prefix: | gpor_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition [Line Items] for Changes In Standardized Measure of Discontinued Future Net Cash Flows [Table] + References No definition available. + Details
Name: | gpor_ChangesInStandardizedMeasureofDiscontinuedFutureNetCashFlowsLineItems
Namespace Prefix: | gpor_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Net change in sales and transfer prices and in production (lifting) costs related to future production and in the evaluation of the costs that will be required in future periods to make it possible to extract or process proved oil and gas reserves. + References No definition available. + Details
Name: | gpor_NetChangesInPricesProductionCostsAndDevelopment
Namespace Prefix: | gpor_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of decrease in standardized measure of discounted future net cash flow as a result of sales of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
Name: | srt_DecreaseDueToSalesOfMineralsInPlace
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of extensions, discoveries and improved recovery of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
Name: | srt_ExtensionsDiscoveriesAdditionsAndImprovedRecoveryLessRelatedCosts
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in the estimated future income tax on future pretax net cash flows related to the entity's proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 + Details
Name: | srt_IncreaseDecreaseInFutureIncomeTaxExpenseEstimatesOnFutureCashFlowsRelatedToProvedOilAndGasReserves
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase in standardized measure of discounted future net cash flow as a result of purchases of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 + Details
Name: | srt_IncreaseDueToPurchasesOfMineralsInPlace
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase in standardized measure of discounted future net cash flow as a result of previously estimated development costs incurred. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 + Details
Name: | srt_PreviouslyEstimatedDevelopmentCostsIncurred
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of revisions of estimated quantity of oil and gas in proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 + Details
Name: | srt_RevisionsOfPreviousQuantityEstimates
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of (increase) decrease in standardized measure of discounted future net cash flow as a result of sales and transfers of oil and gas produced. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 + Details
Name: | srt_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow relating to proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 + Details
Name: | srt_StandardizedMeasureOfDiscountedFutureNetCashFlowOfProvedOilAndGasReservesPeriodIncreaseDecrease
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of accretion of discount for the standardized measure of discounted future net cash flow related to proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35A -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6807758-109447 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 55 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448 + Details
Name: | srt_StandardizedMeasureOfDiscountedFutureNetCashFlowRelatingToProvedOilAndGasReservesAccretionOfDiscount
Namespace Prefix: | srt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=gpor_GrizzlyOilSandsUlcMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |