SCHEDULE I - Parent Company Information - Condensed Statements of Income - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Parent Company
Equity in income of subsidiaries
Equity in income of subsidiaries, tax	$ (30,990)	$ 5,168	$ 4,037

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