Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 130,708	$ 105,219
Marketable securities	315,764	123,439
Restricted cash		200
Prepaid expenses and other current assets	5,902	3,095
Total current assets	452,374	231,953
Property and equipment, net	5,133	3,193
Operating lease right-of-use assets	10,860
Other assets	1,387	4,273
Total assets	469,754	239,419
Current liabilities
Accounts payable	2,555	2,182
Accrued research and development expenses	19,171	10,653
Accrued expenses	11,443	7,568
Total current liabilities	33,169	20,403
Long-term debt	28,370
Operating lease liabilities	9,342
Accrued expenses - long-term		718
Total liabilities	70,881	21,121
Commitments and contingencies
Stockholders' equity (deficit)
Common stock, $0.0001 par value; 700,000,000 shares authorized as of September 30, 2019 and 49,160,177 shares authorized as of December 31, 2018; 66,038,122 shares issued and 60,984,958 shares outstanding as of September 30, 2019, and 15,533,450 shares issued and 8,051,418 shares outstanding as of December 31, 2018	7	2
Additional paid-in capital	678,010	33,853
Accumulated deficit	(279,472)	(153,863)
Accumulated other comprehensive income (loss)	328	(61)
Total stockholders' equity (deficit)	398,873	(120,069)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	469,754	239,419
Series Seed Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference	0	29,200
Series A Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference	0	79,615
Series B Convertible Preferred Stock
Current liabilities
Convertible preferred stock, shares issued, outstanding, and liquidation preference	$ 0	$ 229,552