7. Accounts and Financing Receivables

Trade accounts receivable consisted of the following (in thousands):

	AS OF SEPTEMBER 30,
	2018			2017
Trade accounts receivable	$	15,776		$	10,830
Allowance for doubtful accounts		(1,453	)		(1,395	)
	$	14,323		$	9,435

The allowance for doubtful accounts represents the Company’s best estimate of probable credit losses. The Company determines the allowance based upon historical experience and a review of its balances. Accounts receivable balances are charged off against the allowance whenever it is probable that the receivable will not be recoverable.

Financing receivables are reflected in the following table (in thousands):

	AS OF SEPTEMBER 30,
	2018			2017
Promissory notes	$	5,646		$	4,306
Sales-type lease		5,533			8,581
Total financing receivables		11,179			12,887
Unearned income:
Promissory notes		(95	)		(90	)
Sales-type lease		(237	)		(527	)
Total unearned income		(332	)		(617	)
Total financing receivables, net of unearned income		10,847			12,270
Allowance for doubtful notes		(1,849	)		(1,020	)
Less current portion		(4,258	)		(3,055	)
Non-current financing receivables	$	4,740		$	8,195

Promissory notes receivable are generally collateralized by the products sold, and bear interest at rates ranging up to 5% per year. The promissory notes receivable mature at various times through May 2021. The Company has, on occasion, extended or renewed notes receivable as they mature, but there is no obligation to do so.

The Company entered into a sales-type lease in September 2017 which resulted from the sale of rental equipment. The sales-type lease has a term of three years. Future minimum lease payments required under the lease at September 30, 2018 were $5.8 million, including $0.2 million of unearned income. The Company expects to receive approximately $2.9 million of future minimum lease payments in each of fiscal years 2019 and 2020. The ownership of the equipment will transfer to the lessee at the end of the lease term.