CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 107,459	$ 112,629
Prepaid expenses and other current assets	2,651	3,992
Total current assets	110,110	116,621
Property and equipment, net	1,320	1,472
Restricted cash and other assets	321	324
Total assets	111,751	118,417
Current liabilities:
Accounts payable	1,668	1,334
Accrued expenses	10,224	8,000
Current portion of note payable	131	209
Current portion of deferred revenue	376	566
Total current liabilities	12,399	10,109
Other liabilities	468	613
Total liabilities	12,867	10,722
Commitments and contingencies
Stockholders' equity:
Common stock, $0.001 par value, Authorized — 280,000 shares; Issued and outstanding — 216,095 and 195,625 shares at March 31, 2018 and December 31, 2017, respectively	216	196
Additional paid-in capital	723,257	711,993
Accumulated deficit	(624,589)	(604,494)
Total stockholders' equity	98,884	107,695
Total liabilities and stockholders' equity	111,751	118,417
Series A Preferred Stock
Stockholders' equity:
Preferred stock, $0.01 par value, Authorized — 5,000 shares: Series A convertible preferred stock; Designated — 1,500 shares, Issued and outstanding — 1 share