Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 264,608	$ 297,098
Investments	162,222	185,621
Prepaid expenses and other current assets	3,596	4,626
Total current assets	430,426	487,345
Property and equipment, net	20,989	19,206
Goodwill	30,815	30,815
Restricted cash	1,334	1,568
Deposits	455	455
Operating lease right-of-use assets	1,628	914
Finance lease right-of-use asset	49,507	50,521
Total assets	535,154	590,824
Current liabilities:
Accounts payable and accrued expenses	17,884	25,472
Convertible notes, net of unamortized discount, current	5,102	4,875
Operating lease liabilities, current	792	626
Finance lease liability, current	1,666	1,644
Total current liabilities	25,444	32,617
Convertible notes, net of unamortized discount, non-current	0	35,066
Operating lease liabilities, non-current	1,096	498
Finance lease liability, non-current	19,070	18,988
Other liabilities	107	136
Total liabilities	45,717	87,305
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.01 par value, 120,000,000 shares authorized; 63,448,069 and 60,996,367 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively	634	610
Additional paid-in capital	886,431	825,794
Accumulated other comprehensive loss	(81)	(42)
Accumulated deficit	(397,547)	(322,843)
Total stockholders' equity	489,437	503,519
Total liabilities and stockholders' equity	535,154	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