Statements of Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,960,017)	$ (26,039,550)
Other comprehensive income, net of tax effect:
Unrealized gain on short and long-term investments	1,090	40,267
Comprehensive loss	$ (18,958,927)	$ (25,999,283)