Condensed Balance Sheets - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 19,586,035	$ 13,876,090
Marketable securities	12,984,682	22,632,019
Prepaid and other current assets	1,849,782	1,982,031
Total current assets	34,420,499	38,490,140
Property and equipment, net	336,124	344,734
Other assets	876,129	892,394
Total assets	35,632,752	39,727,268
Current liabilities:
Accounts payable and accrued expenses	2,192,884	2,545,894
Accrued compensation	891,393	1,436,804
Total current liabilities	3,084,277	3,982,698
Note payable	1,000,000	1,000,000
Deferred rent	$ 197,300	$ 204,224
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000,000 shares authorized; 21,098,458 shares issued and 21,075,405 shares outstanding, excluding 23,053 shares subject to repurchase, at March 31, 2016; 19,877,857 shares issued and 19,845,611 shares outstanding, excluding 32,246 shares subject to repurchase, at December 31, 2015	$ 2,108	$ 1,984
Additional paid-in capital	159,514,226	155,441,280
Accumulated other comprehensive income (loss)	5,736	(3,907)
Accumulated deficit	(128,170,895)	(120,899,011)
Total stockholders’ equity	31,351,175	34,540,346
Total liabilities and stockholders’ equity	$ 35,632,752	$ 39,727,268