v3.20.1

Summary of Significant Accounting Policies - Schedule of Estimated Aggregate Amortization Expense (Benefit), Net, Related to Contract-based Intangibles (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Contract Based Intangible Assets And Liabilities Future Amortization Expense Benefit Net [Abstract]
2020	$ (5,542)
2021	(5,265)
2022	(5,265)
2023	(5,265)
2024	(5,265)
Thereafter	$ (39,564)

Contract-based intangible assets and liabilities amortization expense (benefit) net after year five.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesAmortizationExpenseBenefitNetAfterYearFive
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Contract-based intangible assets and liabilities amortization expense (benefit) net next twelve months.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesAmortizationExpenseBenefitNetNextTwelveMonths
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Contract-based intangible assets and liabilities amortization expense (benefit) net year five.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesAmortizationExpenseBenefitNetYearFive
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Contract-based intangible assets and liabilities amortization expense (benefit) net year four.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesAmortizationExpenseBenefitNetYearFour
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Contract-based intangible assets and liabilities amortization expense (benefit) net year three.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesAmortizationExpenseBenefitNetYearThree
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Contract-based intangible assets and liabilities amortization expense (benefit) net year two.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesAmortizationExpenseBenefitNetYearTwo
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Contract-based intangible assets and liabilities future amortization expense (benefit) net.

No definition available.

Name:	felp_ContractBasedIntangibleAssetsAndLiabilitiesFutureAmortizationExpenseBenefitNetAbstract
Namespace Prefix:	felp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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