SCHEDULE I - Parent Company Information - Condensed Statements of Income - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Parent Company [Member]
Equity in income of subsidiaries
Equity in income of subsidiaries, tax	$ 13,323	$ (30,990)	$ 5,168

Represents the tax amount on earnings (losses) of affiliates and subsidiaries during the period.

No definition available.

Name:	wlfc_TaxOnEarningsLossesOfAffiliatesAndSubsidiaries
Namespace Prefix:	wlfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration