Investments - Summarized Financial Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenue		$ 66,472	$ 74,983	$ 127,597	$ 156,592
Expenses		67,646	66,194	129,943	139,479
Net income (loss)		58	5,372	(1,274)	9,658
Statement of Financial Position [Abstract]
Total assets	[1]	2,584,976		2,584,976			$ 2,364,948
Total liabilities	[2]	2,166,523		2,166,523			1,951,211
Total WMES net equity		368,689	357,868	368,689	357,868	$ 372,412	364,015	$ 353,007	$ 350,338
WMES
Income Statement [Abstract]
Revenue		4,885	11,804	9,646	19,915
Expenses		6,606	10,425	12,775	18,179
Net income (loss)		(1,721)	$ 1,379	(3,129)	$ 1,736
Statement of Financial Position [Abstract]
Total assets		298,019		298,019			303,886
Total liabilities		217,097		217,097			219,836
Total WMES net equity		$ 80,922		$ 80,922			$ 84,050

[1] Total assets at June 30, 2021 and December 31, 2020, respectively, include the following assets of variable interest entities (“VIEs”) that can only be used to settle the liabilities of the VIEs: Restricted cash $212,734 and $35,262; Equipment $1,216,186 and $1,037,684; Maintenance Rights $4,317 and $767; Inventory $4,367 and $5,437; Notes receivable $132,134 and $26,392; and Other assets $4,791 and $558, respectively.

[2] Total liabilities at June 30, 2021 and December 31, 2020, respectively, include the following liabilities of VIEs for which the VIEs’ creditors do not have recourse to Willis Lease Finance Corporation: Debt obligations $1,220,448 and $907,550, respectively.