Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 135,089	$ 105,219
Marketable securities	266,740	123,439
Restricted cash	0	200
Prepaid expenses and other current assets	7,488	3,095
Total current assets	409,317	231,953
Property and equipment, net	5,425	3,193
Operating lease right-of-use assets	10,303
Other assets	1,559	4,273
Total assets	426,604	239,419
Current liabilities
Accounts payable	956	2,182
Accrued research and development expenses	19,258	10,653
Accrued expenses and other current liabilities	16,709	7,568
Total current liabilities	36,923	20,403
Long-term debt	28,459
Operating lease liabilities - long-term	8,737
Accrued expenses - long-term		718
Total liabilities	74,119	21,121
Commitments and contingencies
Stockholders' equity (deficit)
Common stock, $0.0001 par value; 700,000,000 shares authorized as of December 31, 2019 and 49,160,177 shares authorized as of December 31, 2018; 66,284,003 shares issued and 61,635,477 shares outstanding as of December 31, 2019, and 15,533,450 shares issued and 8,051,418 shares outstanding as of December 31, 2018	7	2
Additional paid-in capital	686,390	33,853
Accumulated deficit	(334,170)	(153,863)
Accumulated other comprehensive income (loss)	258	(61)
Total stockholders' equity (deficit)	352,485	(120,069)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 426,604	239,419
Series Seed Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference		29,200
Series A Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference		79,615
Series B Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference		$ 229,552