Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 245,644	$ 297,098
Investments	175,815	185,621
Prepaid expenses and other current assets	3,610	4,626
Total current assets	425,069	487,345
Property and equipment, net	22,090	19,206
Goodwill	30,815	30,815
Restricted cash	1,334	1,568
Deposits	455	455
Operating lease right-of-use assets	1,467	914
Finance lease right-of-use asset	49,011	50,521
Total assets	530,241	590,824
Current liabilities:
Accounts payable and accrued expenses	22,008	25,472
Convertible notes, net of unamortized discount, current	0	4,875
Operating lease liabilities, current	804	626
Finance lease liability, current	1,677	1,644
Total current liabilities	24,489	32,617
Convertible notes, net of unamortized discount, non-current	0	35,066
Operating lease liabilities, non-current	891	498
Finance lease liability, non-current	19,109	18,988
Other liabilities	94	136
Total liabilities	44,583	87,305
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.01 par value, 120,000,000 shares authorized; 64,442,601 and 60,996,367 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively	644	610
Additional paid-in capital	932,776	825,794
Accumulated other comprehensive loss	(97)	(42)
Accumulated deficit	(447,665)	(322,843)
Total stockholders' equity	485,658	503,519
Total liabilities and stockholders' equity	530,241	590,824
Series A Convertible Preferred Shares [Member]
Stockholders' equity:
Preferred stock	0	0
Series B Convertible Preferred Shares [Member]
Stockholders' equity:
Preferred stock	$ 0	$ 0