CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 104,416,000	$ 217,431,000
Short-term investments	84,233,000	0
Prepaid expenses and other current assets	3,003,000	2,133,000
Total current assets	191,652,000	219,564,000
Property and equipment, net	36,153,000	37,002,000
Right-of-use assets	5,618,000	5,897,000
Restricted cash	1,274,000	1,274,000
Total assets	234,697,000	263,737,000
Current liabilities:
Accounts payable	4,878,000	4,722,000
Accrued expenses and other liabilities	5,423,000	9,803,000
Operating lease liabilities	2,323,000	2,501,000
Deferred revenue	5,184,000	5,632,000
Total current liabilities	17,808,000	22,658,000
Non-current liabilities:
Operating lease liabilities, net of current portion	12,498,000	12,941,000
Deferred revenue, net of current portion	3,562,000	32,143,000
Total liabilities	33,868,000	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 March 31, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value; 200,000,000 shares authorized; 50,487,649 and 50,268,666 shares issued as of March 31, 2021 and December 31, 2020, respectively; and 50,485,569 and 50,265,575 shares outstanding as of March 31, 2021 and December 31, 2020, respectively	5,000	5,000
Additional paid-in capital	530,288,000	524,358,000
Accumulated other comprehensive loss	(23,000)
Accumulated deficit	(329,441,000)	(328,368,000)
Total stockholders’ equity	200,829,000	195,995,000
Total liabilities and stockholders' equity	$ 234,697,000	$ 263,737,000