Condensed Consolidated Balance Sheets - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 6,664,508	$ 8,077,539
Restricted cash	5,000,000	5,000,000
Marketable investment securities	4,880,876	7,173,037
Accrued interest income	10,854	38,514
Prepaid and other current assets	754,504	520,113
Total current assets	17,310,742	20,809,203
Property and equipment, net of accumulated depreciation of $1,136,283 and $1,124,700, respectively	7,415	18,997
Other assets	23,753	23,753
Total assets	17,341,910	20,851,953
Current liabilities:
Accounts payable	1,360,446	671,280
Accrued expenses	540,954	487,135
Debt - current portion	3,333,333	3,333,333
Total current liabilities	5,234,733	4,491,748
Debt - non-current portion	4,601,837	6,926,532
Total liabilities	9,836,570	11,418,280
Commitments and contingencies (notes 5 and 10)
Stockholders' equity:
Common stock, par value $0.0001 per share, 100,000,000 shares authorized; 25,033,482 and 21,737,196 issued and 25,027,772 and 21,731,486 outstanding	2,503	2,174
Additional paid-in capital	155,318,402	147,533,019
Treasury stock at cost, 5,710 shares	(40,712)	(40,712)
Accumulated other comprehensive income (loss)	261	(963)
Accumulated deficit	(147,775,114)	(138,059,845)
Total stockholders' equity	7,505,340	9,433,673
Total liabilities and stockholders' equity	$ 17,341,910	$ 20,851,953

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).