Statements of Comprehensive Loss - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (9,050,435)	$ (5,308,760)	$ (17,447,496)	$ (10,399,881)
Other comprehensive income/(loss):
Unrealized gain/(loss) on marketable securities	13,826	107	15,272	(4,769)
Total other comprehensive income/(loss)	13,826	107	15,272	(4,769)
Comprehensive loss	$ (9,036,609)	$ (5,308,653)	$ (17,432,224)	$ (10,404,650)