Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities:
Net loss	$ (18,584)	$ (15,516)
Adjustments to reconcile net loss to net cash used by operating activities:
Depreciation and amortization expense	591	537
Non-cash interest	651	296
Stock-based compensation	656	625
Provision for bad debt expense	1,290	0
Loss on debt extinguishment	0	1,333
Employee stock purchase plan compensation	0	103
Changes in operating assets and liabilities:
Accounts receivable	1,795	(469)
Inventory	(1,037)	(1,954)
Prepaid expenses and other current assets	244	288
Accounts payable	150	2,257
Accrued expenses and contract liabilities	(1,006)	(368)
Net cash used in operating activities	(15,250)	(12,868)
Investing Activities:
Purchases of property and equipment	0	(30)
Net cash used in investing activities	0	(30)
Financing activities:
Proceeds from issuance of term debt, net of issuance costs	0	19,207
Repayment of term-loan debt	(5,000)	(10,812)
Proceeds from PPP Loan	1,775	0
Proceeds from borrowing from line of credit	760	1,106
Repayments of borrowing from line of credit	(2,258)	(306)
Proceeds from sale of common stock, net of offering costs	16,366	2,410
Proceeds from sale of common stock under employee stock purchase plan	21	0
Proceeds from warrant and option exercises	3,469	65
Net cash provided by financing activities	15,133	11,670
Net decrease in cash and cash equivalents	(117)	(1,228)
Cash and cash equivalents at beginning of period	17,311	16,523
Cash and cash equivalents at end of period	17,194	15,295
Supplemental cash flow disclosures:
Cash paid for interest	715	245
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment costs incurred but not paid included in accounts payable and accrued expenses	0	9
Fair value of warrants issued with debt	0	630
Transfer of instruments and servers from inventory to property and equipment	1,191	0
Issue common stock for covenant waiver	300
Fair value of stock issued with debt	$ 0	$ 202