Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (49,450)	$ (69,484)	$ (82,764)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash other income/expense, net	424	50	(40)
Non-cash interest income			22
Non-cash interest expense	404	636	519
Loss on extinguishment of debt		2,757
Depreciation and amortization expense	356	417	396
Decrease in right-of-use assets	281	403	374
Stock-based compensation	3,291	5,219	9,748
Other, net	(6)	62	48
Changes in operating assets and liabilities:
(Increase)/decrease in other non-current assets	(10)	8	50
(Increase)/decrease in accounts receivable, net and other receivables and prepaid expenses	(8,117)	(5,887)	2,582
Increase in inventory	(8,686)	(5,141)	(682)
Increase/(decrease) in accounts payable	1,581	(1,813)	1,310
Increase/(decrease) in accrued expenses and other liabilities	946	714	(3,209)
Increase/(decrease) in deferred revenue	(376)	750
Decrease in other non-current liabilities	(189)	(2)	(172)
Decrease in income tax liabilities	(6)	(20)	(74)
Net cash used in operating activities	(59,557)	(71,331)	(71,892)
Cash flows from investing activities
Purchases of plant and equipment and intangible assets	(25)	(113)	(61)
Other	(56)	(161)
Other			392
Net cash (used in) provided by investing activities	(81)	(274)	331
Cash flows from financing activities
Proceeds from exercise of warrants		665
Proceeds from issuance of ordinary shares and warrants	27,911	53,460	20,138
Proceeds from at-the-market facility	42,280	7,520	27,945
Proceeds from long-term debt, net of issuance costs			9,980
Proceeds from employee stock purchase plan		43	372
Repayments of long-term borrowings		(30,000)
Equity transaction costs	(3,825)	(4,764)	(2,360)
Net cash provided by financing activities	66,366	26,924	56,075
Effects of exchange rate changes on the balance of cash held in foreign currencies	(484)	(140)	(106)
Net increase/(decrease) in cash, cash equivalents and restricted cash	6,244	(44,821)	(15,592)
Cash, cash equivalents, and restricted cash at beginning of year	41,590	86,411	102,003
Cash, cash equivalents and restricted cash at end of year	47,834	41,590	86,411
Supplemental disclosure of cash flow information:
Interest paid	497	1,396	2,560
Taxes paid	513	4	11
Equity transaction costs included in accounts payable and accrued expenses	$ 712	$ 765	$ 552