Supplemental Cash Flow Information - Supplemental Cash Flow Information (Details) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($)
Supplemental disclosures of non-cash investing activities:
Depreciation, depletion and amortization capitalized into development costs	$ 3,180

Depreciation depletion and amortization capitalized into development costs.

No definition available.

Name:	felp_DepreciationDepletionAndAmortizationCapitalizedIntoDevelopmentCosts
Namespace Prefix:	felp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration