Condensed Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenues:
Collaboration revenue	$ 6,998,076
Total revenues	6,998,076
Operating expenses:
Research and development	7,925,711	$ 4,698,462
General and administrative	2,763,025	2,576,127
Total operating expenses	10,688,736	7,274,589
Loss from operations	(3,690,660)	(7,274,589)
Other income (expense):
Interest income	170,841	26,978
Interest expense	(97,327)	(17,500)
Other expense	(5,599)	(6,773)
Total other income	67,915	2,705
Net loss	(3,622,745)	(7,271,884)
Other comprehensive income (loss):
Net unrealized (losses) gains on marketable securities	(13,017)	9,643
Comprehensive loss	$ (3,635,762)	$ (7,262,241)
Net loss per share, basic and diluted	$ (0.14)	$ (0.35)
Weighted average shares outstanding used in computing net loss per share, basic and diluted	26,162,958	20,626,044