BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 76,746	$ 115,069
Receivables	7,626	4,665
Prepaid expenses and other current assets	5,035	10,855
Total current assets	89,407	130,589
Property and equipment, net	11,606	10,231
Operating Lease, Right-of-Use Asset	5,371	4,650
Deposits	365	130
Other non-current assets	16	745
Total assets	106,765	146,345
Current liabilities:
Accounts payable	982	960
Accrued expenses	11,846	16,589
Lease liability - current portion	765	819
Total current liabilities	13,593	18,368
Lease liability - noncurrent portion	4,891	3,995
Total liabilities	18,484	22,363
Commitments and contingencies (Note 7)
Stockholders' equity:
Common stock, $0.001 par value; 350,000,000 shares authorized; 215,559,148 and 214,591,906 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively	216	215
Additional paid-in capital	896,390	887,868
Accumulated deficit	(808,325)	(764,101)
Total stockholders' equity	88,281	123,982
Total liabilities and stockholders' equity	$ 106,765	$ 146,345

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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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).