Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (12,124)	$ (19,488)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	112	201
Non-cash interest expense related to notes payable		223
Stock-based compensation expense	480	2,723
Gain from modification of operating lease	(68)
Gain on asset disposal	(71)
Changes in operating assets and liabilities:
Accounts receivable	(203)	457
Inventory	806	(1,600)
Prepaid expenses and other assets	927	262
Accounts payable	(452)	(518)
Accrued expenses and other liabilities	(559)	(2,387)
Deferred revenue		(6)
Operating lease right-of-use assets	360	342
Operating lease liabilities	(363)	(328)
Net cash used in operating activities	(11,155)	(20,119)
Investing activities
Proceeds from sale of property and equipment	130
Purchases of property and equipment		(98)
Net cash provided by (used in) investing activities	130	(98)
Financing activities
Proceeds from sale of common stock and prefunded warrants under a concurrent private placement and registered direct offering, net of issuance costs	15,931
Proceeds from issuance of stock under stock plans	1
Net cash provided by financing activities	15,932
Net increase (decrease) in cash, cash equivalents and restricted cash	4,907	(20,217)
Cash, cash equivalents and restricted cash at beginning of period	21,938	108,475
Cash, cash equivalents and restricted cash at end of period	$ 26,845	88,258
Supplemental cash flow disclosures from investing activities
Cash paid for interest		$ 539