CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 116,313,000	$ 217,431,000
Short-term investments	96,980,000	0
Prepaid expenses and other current assets	4,644,000	2,133,000
Total current assets	217,937,000	219,564,000
Property and equipment, net	34,379,000	37,002,000
Right-of-use assets	5,328,000	5,897,000
Restricted cash	1,274,000	1,274,000
Total assets	258,918,000	263,737,000
Current liabilities:
Accounts payable	5,696,000	4,722,000
Accrued expenses and other liabilities	7,689,000	9,803,000
Operating lease liabilities	2,142,000	2,501,000
Deferred revenue	4,007,000	5,632,000
Total current liabilities	19,534,000	22,658,000
Non-current liabilities:
Operating lease liabilities, net of current portion	12,047,000	12,941,000
Deferred revenue, net of current portion	2,760,000	32,143,000
Total liabilities	34,341,000	67,742,000
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized; no shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value; 200,000,000 shares authorized; 57,088,026 and 50,268,666 shares issued as of June 30, 2021 and December 31, 2020, respectively; and 57,086,957 and 50,265,575 shares outstanding as of June 30, 2021 and December 31, 2020, respectively	6,000	5,000
Additional paid-in capital	584,510,000	524,358,000
Accumulated other comprehensive loss	2,000
Accumulated deficit	(359,941,000)	(328,368,000)
Total stockholders’ equity	224,577,000	195,995,000
Total liabilities and stockholders' equity	$ 258,918,000	$ 263,737,000