Annual report pursuant to Section 13 and 15(d)

Long-Term Debt (Total Interest Expense) (Details)

v2.4.1.9
Long-Term Debt (Total Interest Expense) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Debt Disclosure [Abstract]      
Cash paid for interest $ 28,646us-gaap_InterestPaid $ 24,270us-gaap_InterestPaid $ 1,404us-gaap_InterestPaid
Change in accrued interest 3,875gpor_DebtInstrumentIncreaseDecreaseAccruedInterest (969)gpor_DebtInstrumentIncreaseDecreaseAccruedInterest 4,155gpor_DebtInstrumentIncreaseDecreaseAccruedInterest
Write-off of deferred loan costs 0us-gaap_WriteOffOfDeferredDebtIssuanceCost 0us-gaap_WriteOffOfDeferredDebtIssuanceCost 1,143us-gaap_WriteOffOfDeferredDebtIssuanceCost
Capitalized interest (9,687)us-gaap_InterestCostsCapitalized (7,132)us-gaap_InterestCostsCapitalized 0us-gaap_InterestCostsCapitalized
Amortization of loan costs 1,685us-gaap_AmortizationOfFinancingCosts 1,012us-gaap_AmortizationOfFinancingCosts 640us-gaap_AmortizationOfFinancingCosts
Amortization of note discount and premium (533)us-gaap_AmortizationOfDebtDiscountPremium 298us-gaap_AmortizationOfDebtDiscountPremium 59us-gaap_AmortizationOfDebtDiscountPremium
Other 0gpor_InterestExpenseDebtOther 11gpor_InterestExpenseDebtOther 57gpor_InterestExpenseDebtOther
Total interest expense $ 23,986us-gaap_InterestExpenseDebt $ 17,490us-gaap_InterestExpenseDebt $ 7,458us-gaap_InterestExpenseDebt