Condensed Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating expenses:
Research and development	$ 4,698,462	$ 3,883,613
General and administrative	2,576,127	2,081,309
Total operating expenses	7,274,589	5,964,922
Other income (expense):
Interest income	26,978	11,419
Interest expense	(17,500)	(17,500)
Other expense	(6,773)	(8,661)
Total other income (expense)	2,705	(14,742)
Net loss	(7,271,884)	(5,979,664)
Other comprehensive income (loss):
Net unrealized gains on marketable securities	9,643	10,758
Comprehensive loss	$ (7,262,241)	$ (5,968,906)
Net loss per share, basic and diluted	$ (0.35)	$ (0.38)
Weighted average shares outstanding used in computing net loss per share, basic and diluted	20,626,044	15,581,886