Trade accounts receivable, net are reflected in the following table (in thousands):

	December 31, 2019			September 30, 2019
Trade accounts receivable	$	33,641		$	25,144
Allowance for doubtful accounts		(960	)		(951	)
Total	$	32,681		$	24,193

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 current review of its accounts receivable balances. Accounts receivable balances are charged off against the allowance whenever it is probable that the receivable balance will not be recoverable.

Trade accounts receivable at December 31, 2019 and September 30, 2019 includes $8.7 million and $8.5 million, respectively, due from an international seismic marine customer that, as of December 31, 2019 rented a significant amount of marine nodal equipment from the Company. The Company has experienced cash collection difficulties with this customer throughout fiscal year 2019 and into the first quarter of fiscal year 2020 due to the customer’s inability to generate sufficient cash flows to pay its obligations in a timely manner. In November 2019, the Company accepted from the customer a plan to bring its unpaid invoices to a satisfactory status. The most recent payment made by the customer prior to the plan was $1.4 million in November 2019. The customer did not make any of the scheduled payments as detailed in that plan. In late November 2019, the Company ceased recognizing revenue from this customer and expects to continue to do so until the customer demonstrates its ability to routinely service its debts owed to the Company in the ordinary course of business. At December 31, 2019, the total debt contractually owed by the customer to the Company is $10.2 million; however, the trade accounts receivable of $8.7 million on the Company’s balance sheet at December 31, 2019 excludes $1.5 million of unrecognized revenue invoiced by the Company during the quarter ended December 31, 2019. Prior to the customer missing the first scheduled payment in late November, the Company recognized $2.5 million of revenue from this customer for the quarter ended December 31, 2019.

Subsequent to December 31, 2019, the Company has commenced negotiations with the customer to enter into an agreement requiring the customer to pay a portion of the trade accounts receivable in the near term, to pay all rental payments going forward on a current basis and convert the remaining amount owed into a debt instrument secured by certain of the customer’s assets. The Company expects to finalize the agreement with the customer in its second quarter ending March 31, 2020.

While the Company has significant concerns about the ultimate collection of its accounts receivable from this customer, the Company has not provided any additional bad debt reserves toward its outstanding accounts receivable balance from this customer due to the on-going negotiations. If it becomes probable (in the Company’s judgment) that the customer is unable to generate cash flows sufficient to satisfy the customer’s obligations from the variety of options available to it, the Company will record additional bad debt reserves. The current negotiations may not lead to a definitive agreement being entered into; or the fair market value of the collateral securing the debt under the agreement may not equal or exceed the balance of accounts receivable owed by the customer; or the customer may not meet it’s payment obligations. If any of these situations occur, the Company could record a significant bad debt reserve as soon as the second quarter of fiscal year 2020.

	December 31, 2019			September 30, 2019
Promissory notes	$	607		$	780
Sales-type lease		2,054			2,692
Total financing receivables		2,661			3,472
Unearned income:
Sales-type lease		(28	)		(55	)
Total unearned income		(28	)		(55	)
Total financing receivables, net of unearned income		2,633			3,417
Less current portion		(2,517	)		(3,233	)
Non-current financing receivables	$	116		$	184

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 resulting 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 December 31, 2019 were $2.1 million, including $0.1 million of unearned income. The future minimum lease payments are due in fiscal year 2020. Interest income earned on the lease for the three months ended December 31, 2019 and 2018 was $32,000 and $0.1 million, respectively. The ownership of the equipment will transfer to the lessee at the end of the lease term.