Trading Activities and Related Risks (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Trading Activities and Related Risks
Securities owned, deposited with trading counterparties at fair value	$ 9,500,412	$ 12,395,634
FCMs, interbank market makers and swap counterparties
Trading Activities and Related Risks
Required margin and good faith deposits, low end of the range (as a percent)	5.00%
Required margin and good faith deposits, high end of the range (as a percent)	35.00%
Securities owned, deposited with trading counterparties at fair value	$ 9,500,412	$ 12,395,634
Securities owned, deposited with trading counterparties, percent of net asset value	3.93%	4.15%
Cash deposited with trading counterparties	$ 18,483,321	$ 15,838,709
Cash deposited with trading counterparties, percent of net asset value	7.65%	5.31%

Amount of cash on deposit with trading counterparties.

No definition available.

Name:	gpff_CashDepositedWithTradingCounterparties
Namespace Prefix:	gpff_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cash deposited with trading counterparties as a percent of net asset value.

+ References

No definition available.

+ Details

Name:	gpff_CashDepositedWithTradingCounterpartiesPercentOfAssetValue
Namespace Prefix:	gpff_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	gpff_DepositsWithBrokerDealersLineItems
Namespace Prefix:	gpff_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value, as of the balance sheet date, of financial instruments owned by the entity and pledged to counterparties as collateral. Excludes derivative contracts.

+ References

No definition available.

+ Details

Name:	gpff_FinancialInstrumentsExcludingDerivativesOwnedAndPledgedAsCollateralAtFairValue
Namespace Prefix:	gpff_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Securities owned and pledged as collateral to satisfy margin requirements with broker-dealers as a percent of net asset value.

+ References

No definition available.

+ Details

Name:	gpff_FinancialInstrumentsOwnedAndPledgedAsCollateralAtFairValuePercentOfNetAssetValue
Namespace Prefix:	gpff_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the high end of the range of percentage of net asset value that is required to maintain as margin and good faith deposits with broker-dealers.

+ References

No definition available.

+ Details

Name:	gpff_MarginAndGoodFaithDepositsWithBrokerDealersPercentageOfNetAssetValueHighEndOfRange
Namespace Prefix:	gpff_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the low end of the range of percentage of net asset value that is required to maintain as margin and good faith deposits with broker-dealers.

+ References

No definition available.

+ Details

Name:	gpff_MarginAndGoodFaithDepositsWithBrokerDealersPercentageOfNetAssetValueLowEndOfRange
Namespace Prefix:	gpff_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_CounterpartyNameAxis=gpff_FuturesCommissionMerchantsInterbankMarketMakersAndSwapCounterpartiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: