Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 47,299	$ 62,424
Short-term investments	316,544	367,305
Lease incentive receivables	16,196	0
Prepaid expenses and other current assets	6,233	4,709
Total current assets	386,272	434,438
Operating lease right-of-use assets	101,876	19,376
Property and equipment, net	31,589	27,725
Restricted cash	6,282	999
Deposit and other long-term assets	128	29
Total assets	526,147	482,567
Current liabilities:
Accounts payable	2,259	2,810
Accrued expenses and other current liabilities	14,086	13,588
Lease liability, current portion	4,185	4,473
Total current liabilities	20,530	20,871
Lease liability, net of current portion	125,361	26,235
Other non-current liabilities	1,114	1,114
Total liabilities	147,005	48,220
Stockholders’ equity:
Preferred stock	0	0
Common stock	10	10
Additional paid-in capital	954,854	937,134
Accumulated other comprehensive loss	(417)	(261)
Accumulated deficit	(575,305)	(502,536)
Total stockholders’ equity	379,142	434,347
Total liabilities and stockholders' equity	$ 526,147	$ 482,567