Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 160,020	$ 57,226
Marketable securities	437,351	222,500
Accounts receivable	2,130	4,620
Prepaid expenses and other current assets	17,016	5,135
Total current assets	616,517	289,481
Marketable securities - noncurrent		4,746
Property and equipment, net	15,943	17,996
Operating lease right-of-use assets	39,114	19,137
Other assets	4,748	2,920
Total Assets	676,322	334,280
Current Liabilities:
Accounts payable	10,460	3,941
Accrued expenses	25,554	13,273
Current portion of operating lease liability	5,696	5,745
Current portion of deferred revenue	22,544	12,674
Total current liabilities	64,254	35,633
Deferred revenue, net of current portion	51,387	16,136
Long-term operating lease liability	33,609	12,630
Commitments and contingencies (Note 8)
Stockholders’ Equity:
Common stock, $0.0001 par value; 120,000,000 shares authorized; 66,234,056 and 50,198,044 shares issued and outstanding at December 31, 2020 and 2019, respectively	7	5
Additional paid-in capital	962,173	570,493
Accumulated other comprehensive income	1	261
Accumulated deficit	(435,109)	(300,878)
Total stockholders’ equity	527,072	269,881
Total Liabilities and Stockholders’ Equity	$ 676,322	$ 334,280