Name:	us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

Name:	us-gaap_RestrictedCashAndInvestmentsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents money paid in advance to protect the provider of a product or service, such as a lessor, against damage or nonpayment by the buyer or tenant (lessee) during the term of the agreement. Such damages may include physical damage to the property, theft of property, and other contractual breaches. Security deposits held may be interest or noninterest bearing.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Name:	us-gaap_SecurityDepositLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents the minimum amount of cash from maintenance reserve payments required to be held in a restricted cash account.

No definition available.

Name:	wlfc_MinimumCashFromMaintenanceReservePaymentsRequiredToBeHeldInRestrictedCashAccount
Namespace Prefix:	wlfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the maintenance obligation period for which cash reserve payments are held in the restricted cash account.

No definition available.

Name:	wlfc_ProjectedMaintenanceObligationPeriod
Namespace Prefix:	wlfc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the maintenance obligation period for which cash reserve payments are held in the restricted cash account for the purpose of security deposit.

No definition available.

Name:	wlfc_ProjectedMaintenanceObligationPeriodForSecurityDeposit
Namespace Prefix:	wlfc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_DebtInstrumentAxis=wlfc_WestIIINotesMember
Namespace Prefix:
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Balance Type:
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Name:	us-gaap_DebtInstrumentAxis=wlfc_WESTIVNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_DebtInstrumentAxis=wlfc_WESTVNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_DebtInstrumentAxis=wlfc_WESTVINotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_DebtInstrumentAxis=wlfc_WESTIIINotesWESTIVNotesAndWESTVNotesMember
Namespace Prefix:
Data Type:	na
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Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
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