CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 46,213,413	$ 51,574,932
Short-term investments	70,519,061	78,083,604
Prepaid expenses and other current assets	3,672,428	1,944,751
Total current assets	120,404,902	131,603,287
Property and equipment, net	3,828,104	3,154,205
Deferred offering costs	3,072,558	1,000,262
Restricted cash	1,772,587	1,772,587
TOTAL ASSETS	129,078,151	137,530,341
CURRENT LIABILITIES:
Accounts payable	3,776,474	2,538,057
Accrued expenses and other liabilities	2,258,037	2,860,025
Deferred rent		122,601
Deferred revenue	3,407,555	3,341,063
Total current liabilities	9,442,066	8,861,746
NON-CURRENT LIABILITIES:
Deferred rent, net of current portion	1,552,358	290,923
Deferred revenue, net of current portion	29,846,448	30,069,563
Total liabilities	40,840,872	39,222,232
COMMITMENTS (NOTE 7)
CONVERTIBLE PREFERRED STOCK:
Total convertible preferred stock	137,762,160	137,762,160
STOCKHOLDERS’ DEFICIT:
Common stock, $0.0001 par value; 170,000,000 shares authorized as of March 31, 2018 and December 31, 2017; 2,928,313 and 2,902,109 shares issued as of March 31, 2018 and December 31, 2017, respectively; and 2,697,352 and 2,637,011 shares outstanding as of March 31, 2018 and December 31, 2017, respectively	270	264
Additional paid-in capital	1,264,652	799,859
Accumulated other comprehensive loss	(86,165)	(73,308)
Accumulated deficit	(50,703,638)	(40,180,866)
Total stockholders’ deficit	(49,524,881)	(39,454,051)
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ DEFICIT	129,078,151	137,530,341
Series A Convertible Preferred Stock
CONVERTIBLE PREFERRED STOCK:
Total convertible preferred stock	42,994,550	42,994,550
Series B Convertible Preferred Stock
CONVERTIBLE PREFERRED STOCK:
Total convertible preferred stock	$ 94,767,610	$ 94,767,610