Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 252,540	$ 297,098
Investments	213,813	185,621
Prepaid expenses and other assets	5,469	4,626
Total current assets	471,822	487,345
Property and equipment, net	19,833	19,206
Goodwill	30,815	30,815
Restricted cash	1,461	1,568
Deposits	455	455
Operating lease right-of-use assets	1,787	914
Finance lease right-of-use asset	50,311	50,521
Total assets	576,484	590,824
Current liabilities:
Accounts payable and accrued expenses	33,168	25,472
Convertible notes, net of unamortized discount, current	4,986	4,875
Operating lease liabilities, current	683	626
Finance lease liability, current	1,655	1,644
Total current liabilities	40,492	32,617
Convertible notes, net of unamortized discount, non-current	35,544	35,066
Operating lease liabilities, non-current	1,299	498
Finance lease liabilities, non-current	19,028	18,988
Other liabilities	122	136
Total liabilities	96,485	87,305
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $0.01 par value, 120,000,000 shares authorized; 61,987,799 and 60,996,367 shares issued and outstanding at March 31, 2021 and December 31, 2020, respectively	619	610
Additional paid-in capital	842,477	825,794
Accumulated other comprehensive loss	(75)	(42)
Accumulated deficit	(363,022)	(322,843)
Total stockholders' equity	479,999	503,519
Total liabilities and stockholders' equity	576,484	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