Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 21,091	$ 38,388
Available-for-sale investments, short-term	64,028	33,759
Prepaid expenses and other assets	1,866	2,621
Total current assets	86,985	74,768
Available-for-sale investments, long-term		4,002
Property and equipment, net	2,280	1,421
Other assets	90	333
Total assets	89,355	80,524
Current liabilities:
Accounts payable	2,276	2,606
Accrued expenses	3,103	5,450
Current portion of deferred rent		130
Current portion of long-term debt, net of issuance costs and discount	5,012	339
Total current liabilities	10,391	8,525
Long-term debt, net of current portion and issuance costs and discount	14,719	9,198
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.001 par value; undesignated authorized shares – 5,000,000 at December 31, 2017 and 2016, respectively; Class X Convertible Preferred Stock issued and outstanding shares– 2,285,952 and no shares at December 31, 2017 and 2016, respectively	2
Common stock, $0.001 par value; authorized shares – 150,000,000 as of December 31, 2017 and 2016, respectively; issued and outstanding shares – 29,789,162 and 23,744,832 as of December 31, 2017 and 2016, respectively	30	24
Additional paid-in capital	328,519	278,832
Accumulated other comprehensive loss	(120)	(76)
Accumulated deficit	(264,186)	(215,979)
Total stockholders’ equity	64,245	62,801
Total liabilities and stockholders’ equity	$ 89,355	$ 80,524