Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 43,806	$ 48,750
Prepaid expenses	1,161	2,768
Total current assets	44,967	51,518
Property and equipment, net	13,426	12,330
Other assets	18	18
Total assets	58,411	63,866
Current liabilities:
Accounts payable	2,823	2,050
Accrued expenses	1,857	3,644
Loan payable, current portion	6,190	5,104
Warrant liability	90	172
Total current liabilities	10,960	10,970
Loan payable, long-term	5,887	10,607
Commitments and contingencies
Stockholders' equity:
Common stock, $.0001 par value, authorized 150,000,000 shares; 34,158,004 shares issued and outstanding as of September 30, 2017 and 28,759,731 shares issued and outstanding as of December 31, 2016;	3	3
Additional paid-in capital	257,093	235,754
Accumulated deficit	(215,532)	(193,468)
Total stockholders' equity	41,564	42,289
Total liabilities and stockholders' equity	$ 58,411	$ 63,866

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).

Name:	us-gaap_AccountsPayableCurrent
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).