CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 36,038,391	$ 51,574,932
Short-term investments	201,505,628	78,083,604
Prepaid expenses and other current assets	8,322,324	1,944,751
Total current assets	245,866,343	131,603,287
Property and equipment, net	20,740,518	3,154,205
Deferred offering costs		1,000,262
Restricted cash	1,789,962	1,772,587
Total assets	268,396,823	137,530,341
Current liabilities:
Accounts payable	11,120,883	2,538,057
Accrued expenses and other liabilities	3,847,760	2,860,025
Deferred rent		122,601
Deferred revenue	3,605,332	3,341,063
Total current liabilities	18,573,975	8,861,746
Non-current liabilities:
Deferred rent, net of current portion	7,318,684	290,923
Deferred revenue, net of current portion	29,743,989	30,069,563
Total liabilities	55,636,648	39,222,232
Commitments and contingencies (Note 7)
Convertible preferred stock:
Total convertible preferred stock		137,762,160
Stockholders’ equity (deficit):
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of September 30, 2018 and no shares authorized as of December 31, 2017; no shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock, $0.0001 par value; 200,000,000 and 170,000,000 shares authorized as of September 30, 2018 and December 31, 2017, respectively; 37,494,061 and 2,902,109 shares issued as of September 30, 2018 and December 31, 2017, respectively; and 37,310,063 and 2,637,011 shares outstanding as of September 30, 2018 and December 31, 2017, respectively	3,733	264
Additional paid-in capital	291,171,747	799,859
Accumulated other comprehensive loss	(20,878)	(73,308)
Accumulated deficit	(78,394,427)	(40,180,866)
Total stockholders’ equity (deficit)	212,760,175	(39,454,051)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 268,396,823	137,530,341
Series A Convertible Preferred Stock
Convertible preferred stock:
Total convertible preferred stock		42,994,550
Series B Convertible Preferred Stock
Convertible preferred stock:
Total convertible preferred stock		$ 94,767,610