CONDENSED STATEMENT OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($)	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Deficit	Total
Balance at beginning of period at Dec. 31, 2016			$ (41,196)
Net loss					$ (23,233,313)
Unrealized gain (loss) on securities					6,333
Balance at end of period at Jun. 30, 2017			(34,863)
Balance at beginning of period at Mar. 31, 2017			(53,877)
Net loss					(11,744,728)
Unrealized gain (loss) on securities					19,014
Balance at end of period at Jun. 30, 2017			(34,863)
Cumulative effect of adoption of ASC 606 | ASU 2014-09				$ 339,406	339,406
Balance after adjustment	$ 48,204	$ 404,454,909	(64,433)	(308,615,129)	95,823,551
Balance at beginning of period at Dec. 31, 2017	$ 48,204	404,454,909	(64,433)	(308,954,535)	$ 95,484,145
Balances (in shares) at Dec. 31, 2017	48,203,529
Exercise of stock options (in shares)					561,088
Balance at end of period at Mar. 31, 2018			(79,143)
Balance at beginning of period at Dec. 31, 2017	$ 48,204	404,454,909	(64,433)	(308,954,535)	$ 95,484,145
Balances (in shares) at Dec. 31, 2017	48,203,529
Exercise of stock options	$ 1,074	6,487,057			6,488,131
Exercise of stock options (in shares)	1,073,883
Stock-based compensation	$ 157	2,695,867			2,696,024
Stock-based compensation (in shares)	157,592
Employee stock purchase plan	$ 25	95,045			95,070
Employee stock purchase plan (in shares)	25,352
Issuance of common stock in connection with equity offering	$ 20,536	80,880,045			80,900,581
Issuance of common stock in connection with equity offering (in shares)	20,535,714
Number of shares purchased under ESPP	25,352
Net loss				(20,167,289)	(20,167,289)
Unrealized gain (loss) on securities			30,109		30,109
Balance at end of period at Jun. 30, 2018	$ 69,996	494,612,923	(34,324)	(328,782,418)	$ 165,866,177
Balances (in shares) at Jun. 30, 2018	69,996,070
Balance at beginning of period at Mar. 31, 2018			(79,143)
Exercise of stock options (in shares)					512,795
Net loss					$ (11,564,643)
Unrealized gain (loss) on securities					44,819
Balance at end of period at Jun. 30, 2018	$ 69,996	$ 494,612,923	$ (34,324)	$ (328,782,418)	$ 165,866,177
Balances (in shares) at Jun. 30, 2018	69,996,070