Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current Assets
Cash and cash equivalents	$ 75,437	$ 60,541
Prepaid expenses and other current assets	4,265	1,148
Total current assets	79,702	61,689
Restricted cash	2,430	2,430
Property and equipment, net	470	526
Operating lease right-of-use assets	2,582	2,958
Intangible asset, net	36	97
Other assets	10	10
Total assets	85,230	67,710
Current liabilities
Accounts payable	3,601	2,500
Accrued liabilities	1,615	2,323
Operating lease obligation, current portion	2,373	2,086
Current portion of deferred revenue	4,010	2,552
Total current liabilities	11,599	9,461
Deferred revenue, net of current portion	4,315	3,763
Operating lease obligation, net of current portion	5,258	6,431
Total liabilities	21,172	19,655
Stockholders' equity
Common stock, $0.0001 par value, 100,000,000 shares authorized at June 30, 2021 and December 31, 2020; 20,714,004 and 16,481,099 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively	2	2
Additional paid-in capital	579,819	548,707
Accumulated deficit	(515,763)	(500,654)
Total stockholders' equity	64,058	48,055
Total liabilities and stockholders’ equity	$ 85,230	$ 67,710

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).