Nonrecurring impairment charges related to the write-off of production-related equipment and inventory. This tag is used when an Entity charges this cost to cost of goods sold.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.13)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Stated as a percentage, the estimated or actual value of the asset at the end of its useful life or when it is no longer serviceable (cannot be used for its original purpose) divided by its [historical] capitalized cost.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Number of Engines

+ References

No definition available.

+ Details

Name:	wlfc_NumberOfEngines
Namespace Prefix:	wlfc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
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Balance Type:
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- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_MajorPropertyClassAxis=wlfc_EnginesAndRelatedEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorPropertyClassAxis=wlfc_NewEngineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorPropertyClassAxis=wlfc_AircraftMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorPropertyClassAxis=wlfc_EnginesAndAircraftMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=us-gaap_PropertyAvailableForOperatingLeaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorPropertyClassAxis=wlfc_SparePartPackagesMember
Namespace Prefix:
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Organization and Summary of Significant Accounting Policies - Equipment Held of Operating Lease (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) engine	Dec. 31, 2018 USD ($)
Equipment Held for Operating Lease
Impairment charge	$ 18,220	$ 10,651
Minimum
Equipment Held for Operating Lease
Estimated useful life	3 years
Maximum
Equipment Held for Operating Lease
Estimated useful life	39 years
Engines and related equipment
Equipment Held for Operating Lease
Number of engines \| engine	47
New engine \| Maximum
Equipment Held for Operating Lease
Estimated useful life	25 years
Aircraft \| Minimum
Equipment Held for Operating Lease
Residual value (as a percent)	15.00%
Estimated useful life	13 years
Aircraft \| Maximum
Equipment Held for Operating Lease
Residual value (as a percent)	17.00%
Estimated useful life	20 years
Engines and aircraft
Equipment Held for Operating Lease
Equipment net book value	$ 51,100
Engines and aircraft \| Minimum
Equipment Held for Operating Lease
Estimated useful life	1 month
Engines and aircraft \| Maximum
Equipment Held for Operating Lease
Estimated useful life	79 months
Equipment held for lease
Equipment Held for Operating Lease
Impairment charge	$ 6,400	$ 5,300
Equipment held for lease \| Engines and related equipment
Equipment Held for Operating Lease
Residual value (as a percent)	55.00%
Estimated useful life	15 years
Equipment held for lease \| Spare part packages
Equipment Held for Operating Lease
Residual value (as a percent)	25.00%
Equipment held for lease \| Spare part packages \| Minimum
Equipment Held for Operating Lease
Estimated useful life	14 years
Equipment held for lease \| Spare part packages \| Maximum
Equipment Held for Operating Lease
Estimated useful life	15 years