Future minimum rental payments in aggregate as of the balance sheet date under operating leases.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Future rental payments receivable within one year of the balance sheet date under an operating lease.

+ References

+ Details

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

- Definition

Future rental payments receivable within the fifth year from the balance sheet date under an operating lease.

+ References

+ Details

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

- Definition

Future rental payments receivable within the fourth year from the balance sheet date under an operating lease.

+ References

+ Details

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

- Definition

Future rental payments receivable within the third year from the balance sheet date under an operating lease.

+ References

+ Details

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

- Definition

Future rental payments receivable within the second year from the balance sheet date under an operating lease.

+ References

+ Details

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

- Definition

Future minimum lease payments receivable under operating leases for periods greater than five years following the balance sheet date.

+ References

+ Details

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

- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39896-112707

+ Details

Name:	us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

The amount of property, by major property class, net of accumulated depreciation, subject to or available for lease as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718

+ Details

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

- Definition

The number of units (items of property) under operating lease arrangements.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of geographic regions in which aircraft lessees are domiciled in.

+ References

No definition available.

+ Details

Name:	wlfc_NumberOfGeographicRegionsInWhichAircraftLesseesAreDomiciledIn
Namespace Prefix:	wlfc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_EntityByLocationAxis=us-gaap_EuropeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=us-gaap_AsiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=us-gaap_SouthAmericaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=country_MX
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=country_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=us-gaap_MiddleEastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_EntityByLocationAxis=us-gaap_AfricaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=wlfc_YearOfMaturity2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=wlfc_YearOfMaturity2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=wlfc_YearOfMaturity2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=wlfc_YearOfMaturity2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=wlfc_YearOfMaturity2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Equipment Held for Operating Lease (Details) $ in Thousands	12 Months Ended
Equipment Held for Operating Lease (Details) $ in Thousands	Dec. 31, 2017 USD ($) aircraft item region	Dec. 31, 2016 USD ($) aircraft item	Dec. 31, 2015 USD ($)
Equipment Held for Lease
Number of geographic regions in which aircraft lessees are domiciled in \| region	8
Lease rent revenue	$ 130,369	$ 119,895	$ 108,046
Net book value of equipment held for operating lease	1,342,571	1,136,603
Minimum future payments under non-cancelable leases
2018	110,666
2019	54,245
2020	31,913
2021	16,757
2022	10,652
Thereafter	13,242
Minimum future payments	237,475
Europe
Equipment Held for Lease
Lease rent revenue	50,789	44,650	43,703
Net book value of equipment held for operating lease	444,938	384,661
Asia
Equipment Held for Lease
Lease rent revenue	34,169	34,524	31,569
Net book value of equipment held for operating lease	258,501	265,736
South America
Equipment Held for Lease
Lease rent revenue	11,958	11,504	9,688
Net book value of equipment held for operating lease	111,999	112,268
United States
Equipment Held for Lease
Lease rent revenue	20,307	13,395	9,177
Net book value of equipment held for operating lease	251,959	148,208
Mexico
Equipment Held for Lease
Lease rent revenue	5,409	6,251	6,886
Net book value of equipment held for operating lease	34,399	55,114
Canada
Equipment Held for Lease
Lease rent revenue	4,355	4,049	2,828
Net book value of equipment held for operating lease	28,977	35,199
Middle East
Equipment Held for Lease
Lease rent revenue	3,360	3,674	2,223
Net book value of equipment held for operating lease	61,606	8,971
Africa
Equipment Held for Lease
Lease rent revenue	22	1,848	$ 1,972
Net book value of equipment held for operating lease	2,959	42,949
Off-lease and other
Equipment Held for Lease
Net book value of equipment held for operating lease	$ 147,233	$ 83,497
Equipment held for lease Member \| Engines and related equipment
Equipment Held for Lease
Number of equipments held for lease \| aircraft	225	208
Equipment held for lease Member \| Other leased parts and equipment
Equipment Held for Lease
Number of equipments held for lease \| item	7	5
Equipment held for lease Member \| Aircrafts
Equipment Held for Lease
Number of equipments held for lease \| aircraft	16	11
Month-to-month leases
Equipment Held for Lease
Net book value of equipment held for operating lease	$ 89,795
Leases expiring 2018
Equipment Held for Lease
Net book value of equipment held for operating lease	528,225
Leases expiring 2019
Equipment Held for Lease
Net book value of equipment held for operating lease	236,080
Leases expiring 2020
Equipment Held for Lease
Net book value of equipment held for operating lease	158,264
Leases expiring 2021
Equipment Held for Lease
Net book value of equipment held for operating lease	57,268
Leases expiring 2022
Equipment Held for Lease
Net book value of equipment held for operating lease	33,181
Leases expiring thereafter
Equipment Held for Lease
Net book value of equipment held for operating lease	$ 92,525