Borrowings (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-term debt:
Current portion of long-term debt	$ 129	$ 219	$ 177
Total short-term debt	129	219	177
Long-term debt:
Capital lease obligations	175	232	272
Other unsecured promissory notes	121	248	496
Total	296	480	768
Less: current portion of long-term debt	(129)	(219)	(177)
Total long-term debt	$ 167	$ 261	$ 591

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal, through the balance sheet date and due to be paid more than one year (or one operating cycle, if longer) after the balance sheet date.

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