Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 136,411	$ 142,086
Accounts receivable	4,653	1,789
Prepaid expenses and other current assets	6,382	6,582
Total current assets	147,446	150,457
Property and equipment, net	1,395	1,054
Restricted cash	199	199
Total assets	149,040	151,710
Current liabilities:
Accounts payable	5,306	2,555
Accrued expenses	12,559	7,685
Deferred revenue	660	1,255
Total current liabilities	18,525	11,495
Other long term liabilities	105	162
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, par value $0.001 per share; 5,000 shares authorized; no shares issued and outstanding
Common stock, par value $0.001 per share; 125,000 shares authorized; 51,458 and 36,942 shares issued and outstanding at December 31, 2017 and 2016, respectively	51	37
Additional paid-in capital	592,243	487,148
Accumulated deficit	(461,884)	(347,132)
Total stockholders’ equity	130,410	140,053
Total liabilities and stockholders’ equity	$ 149,040	$ 151,710

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).

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

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.