Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Current Assets
Cash and cash equivalents	$ 131,954	$ 67,329
Short-term investments	472,203	562,108
Short-term investments	461,976	562,108
Prepaid expenses and other assets	11,288	6,663
Total Current Assets	605,218	636,100
Property and equipment, net	72,750	59,159
Operating lease right-of-use assets	55,131	54,756
Long-term investments	10,227
Restricted cash	6,084	5,525
Long-term assets	1,163	12,918
Total Assets	750,573	768,458
Current Liabilities
Accounts payable	13,369	13,513
Accrued expenses	35,774	35,074
Operating lease liabilities - current	5,916	6,284
Total Current Liabilities	55,059	54,871
Non-Current Liabilities
Operating lease liabilities - noncurrent	47,083	45,375
Long-term note payable	1,000
Other liabilities		11,714
Total Non-Current Liabilities	48,083	57,089
Total Liabilities	103,142	111,960
Commitments and contingencies
Stockholders' Equity
Common stock, $0.000041666 par value; 300,000,000 shares authorized, 149,315,299 and 146,874,917 shares issued and outstanding as of March 31, 2021 and December 31, 2020, respectively	6	6
Accumulated other comprehensive income	96	19
Additional paid-in capital	1,552,968	1,486,662
Accumulated deficit	(905,642)	(830,193)
Total Stockholders' Equity	647,431	656,498
Total Liabilities and Stockholders' Equity	750,573	768,458
Series B Convertible Preferred Stock
Stockholders' Equity
Preferred stock, Value	3	4
Total Stockholders' Equity	$ 3	$ 4