CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (8,804,623)	$ (11,363,133)	$ (17,073,018)	$ (20,955,594)
Other comprehensive gain (loss):
Unrealized gain (loss) on available-for-sale securities	6,737	19,885	(4,002)	64,144
Comprehensive loss	$ (8,797,886)	$ (11,343,248)	$ (17,077,020)	$ (20,891,450)