Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 43,191	$ 53,025
Available-for sale investments, short-term	40,735	42,510
Prepaid expenses and other assets	1,964	2,415
Total current assets	85,890	97,950
Available-for sale investments, long-term	12,655	29,814
Property and equipment, net	1,766	1,793
Other assets	175	118
Total assets	100,486	129,675
Current liabilities:
Accounts payable	4,723	3,872
Accrued expenses and other current liabilities	5,414	4,595
Current portion of deferred rent	291	315
Current portion of commercial bank debt	3,489	3,366
Total current liabilities	13,917	12,148
Deferred rent, net of current portion		130
Commercial bank debt, net of current portion		1,776
Other long-term liabilities		571
Commitments and contingencies (Note 3)
Redeemable convertible preferred stock, $0.001 par value; authorized shares – 7,285,456 at June 30, 2016 and December 31, 2015; issued and outstanding shares – none at June 30, 2016 and December 31, 2015
Stockholders’ equity:
Undesignated preferred stock, $0.001 par value; authorized shares – 5,000,000 at June 30, 2016 and December 31, 2015; issued and outstanding shares – none at June 30, 2016 and December 31, 2015
Common stock, $0.001 par value; authorized shares – 150,000,000 at June 30, 2016 and December 31, 2015; issued and outstanding shares – 23,717,683 at June 30, 2016 and 23,670,079 at December 31, 2015	24	24
Additional paid-in capital	276,120	273,321
Accumulated other comprehensive income (loss)	19	(171)
Accumulated deficit	(189,594)	(158,124)
Total stockholders’ equity	86,569	115,050
Total liabilities, redeemable convertible preferred stock and stockholders’ equity	$ 100,486	$ 129,675