4. Equipment under operating leases, net:

The Company’s equipment under operating leases, net consists of the following (in thousands):


	Balance				Depreciation/		Balance
	December 31,				Amortization		March 31,
	2019		Additions		Expense		2020
Equipment under operating leases, net	$	10,159	$	—	$	(369)	$	9,790
Initial direct costs, net of accumulated amortization of $139 thousand at March 31, 2020 and $179 thousand at December 31, 2019		131		—		(19)		112
Total	$	10,290	$	—	$	(388)	$	9,902

Impairment of equipment under operating leases:

As a result of impairment reviews, management determined that no impairment losses existed for the three months ended March 31, 2020 and 2019.

The Company utilizes a straight line depreciation method over the term of the equipment lease for equipment on operating leases currently in its portfolio. Depreciation expense on the Company’s equipment totaled $369 thousand and $318 thousand for the respective three months ended March 31, 2020 and 2019. IDC amortization expense related to the Company’s operating leases totaled $19 thousand and $0 for the three months ended March 31, 2020 and 2019, respectively.

All of the Company’s lease asset purchases and capital improvements were made during the years from 2016 through 2019.

Operating leases:

Property on operating leases consists of the following (in thousands):


	Balance						Balance
	December 31,				Reclassifications		March 31,
	2019		Additions		or Dispositions		2020
Transportation, rail	$	3,657	$	—	$	—	$	3,657
Mining		2,749		—		—		2,749
Construction		1,484		—		—		1,484
Aviation		1,306		—		—		1,306
Paper processing		1,058		—		—		1,058
Marine vessels		1,041		—		—		1,041
Containers		860		—		—		860
Agriculture		742		—		—		742
Materials handling		960		—		—		960
Transportation, other		97		—		—		97
		13,954		—		—		13,954
Less accumulated depreciation		(3,795)		(369)		—		(4,164)
Total	$	10,159	$	(369)	$	—	$	9,790

The average estimated residual value for assets on operating leases was 38% and 37% of the assets’ original cost at March 31, 2020 and December 31, 2019, respectively. There were no operating leases in non-accrual status at both March 31, 2020 and December 31, 2019.

At March 31, 2020, the aggregate amounts of future minimum lease payments receivable are as follows (in thousands):


	Operating
	Leases
Nine months ending December 31, 2020	$	1,355
Year ending December 31, 2021		1,364
2022		1,146
2023		1,091
2024		724
Thereafter		527
	$	6,207

The useful lives for each category of leases is reviewed at a minimum of once per quarter. As of March 31, 2020, the respective useful lives of each category of lease assets in the Company’s portfolio are as follows (in years):


Equipment category		Useful Life
Transportation, rail		35 - 50
Marine vessel		20 - 30
Containers		15 - 20
Aviation		15 - 20
Mining		10 - 15
Paper processing		10 - 15
Agriculture		7 - 10
Construction		7 - 10
Materials handling		7 - 10
Transportation		7 - 10