CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Collaboration revenue	$ 14,465	$ 12,500	$ 30,320	$ 25,000
Total revenue	14,465	12,500	30,320	25,000
Operating expenses:
Research and development	7,624,495	8,655,021	12,879,560	16,649,493
General and administrative	4,631,981	3,305,284	8,409,527	7,050,546
Total operating expenses	12,256,476	11,960,305	21,289,087	23,700,039
Loss from operations	(12,242,011)	(11,947,805)	(21,258,767)	(23,675,039)
Other income, net:
Interest income, net	720,408	233,682	1,133,305	469,133
Other expense, net	(43,040)	(30,605)	(41,827)	(27,407)
Net loss	$ (11,564,643)	$ (11,744,728)	$ (20,167,289)	$ (23,233,313)
Net loss per share -basic and diluted (in dollars per share)	$ (0.17)	$ (0.28)	$ (0.32)	$ (0.55)
Items included in other comprehensive income:
Unrealized gain (loss) and amounts reclassified to net loss on available-for-sale securities	$ 44,819	$ 19,014	$ 30,109	$ 6,333
Other comprehensive income	44,819	19,014	30,109	6,333
Comprehensive loss	$ (11,519,824)	$ (11,725,714)	$ (20,137,180)	$ (23,226,980)
Weighted-average number of common shares used in net loss per share calculation - basic and diluted (in shares)	69,712,883	42,503,584	62,397,454	42,469,337