CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 113,681	$ 88,915
Prepaid expenses and other current assets	5,641	4,843
Total current assets	119,322	93,758
Property and equipment, net	30,263	31,410
Restricted cash, net of current portion	4,170	4,170
Operating right-of-use assets	21,519	22,003
Total assets	175,274	151,341
Current liabilities:
Accounts payable	1,782	2,018
Accrued expenses	7,689	8,870
Deferred revenue	9,117	5,281
Operating lease liabilities	2,333	1,482
Total current liabilities	20,921	17,651
Long-term liabilities:
Deferred revenue, net of current portion	41,746	57,416
Note payable, net of discount	25,230	24,960
Operating lease liabilities, net of current portion	35,306	36,540
Other long-term liabilities	207	207
Total liabilities	123,410	136,774
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock, $0.0001 par value; 150,000,000 shares authorized as of June 30, 2021 and December 31, 2020; 22,272,975 and 18,787,579 shares issued and outstanding as of June 30, 2021 and December 31, 2020, respectively	2	2
Additional paid-in capital	372,069	302,655
Accumulated deficit	(320,207)	(288,090)
Total stockholders’ equity	51,864	14,567
Total liabilities and stockholders’ equity	$ 175,274	$ 151,341