5. 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		December 31,
	2018		Additions		Expense		2019
Equipment under operating leases, net	$	10,001	$	1,494	$	(1,336)	$	10,159
Initial direct costs, net of accumulated amortization of $179 thousand at December 31, 2019 and $148 thousand at December 31, 2018		185		5		(59)		131
Total	$	10,186	$	1,499	$	(1,395)	$	10,290

Impairment of equipment under operating leases:

As a result of impairment reviews, management determined that no impairment losses existed for the years ended December 31, 2019 and 2018.

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 $1.3 million and $1.2 million for the respective years ended December 31, 2019 and 2018. IDC amortization expense related to the Company’s operating leases totaled $59 thousand and $66 thousand for the years ended December 31, 2019 and 2018, 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		December 31,
	2018		Additions		or Dispositions		2019
Transportation, rail	$	3,679	$	—	$	(22)	$	3,657
Mining		1,728		1,021		—		2,749
Construction		1,242		242		—		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		711		249		—		960
Transportation, other		97		—		—		97
		12,464		1,512		(22)		13,954
Less accumulated depreciation		(2,463)		(1,336)		4		(3,795)
Total	$	10,001	$	176	$	(18)	$	10,159

The average estimated residual value for assets on operating leases was 37% and 38% of the assets’ original cost at December 31, 2019 and 2018, respectively. There were no operating leases in non-accrual status at both December 31, 2019 and 2018.

At December 31, 2019, the aggregate amounts of future minimum lease payments receivable are as follows (in thousands):


	Operating
	Leases
Year ending December 31, 2020	$	1,858
2021		1,364
2022		1,146
2023		1,091
2024		724
Thereafter		527
	$	6,710

The useful lives for each category of leases is reviewed at a minimum of once per quarter. As of December 31, 2019, 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