Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 170,847	$ 105,219
Marketable securities	310,374	123,439
Restricted cash		200
Prepaid expenses and other current assets	16,567	3,095
Total current assets	497,788	231,953
Property and equipment, net	4,110	3,193
Operating lease right-of-use assets	11,922
Other assets	2,129	4,273
Total assets	515,949	239,419
Current liabilities
Accounts payable	4,548	2,182
Accrued research and development expenses	12,725	10,653
Accrued expenses	7,879	7,568
Total current liabilities	25,152	20,403
Operating lease liabilities	10,537
Accrued expenses - long-term		718
Total liabilities	35,689	21,121
Commitments and contingencies - Note 10
Stockholders' equity (deficit)
Common stock, $0.0001 par value; 700,000,000 shares authorized as of March 31, 2019 and 49,160,177 shares authorized as of December 31, 2018; 65,891,910 shares issued and 60,029,470 shares outstanding as of March 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	666,648	33,853
Accumulated deficit	(186,474)	(153,863)
Accumulated other comprehensive income (loss)	79	(61)
Total stockholders' equity (deficit)	480,260	(120,069)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 515,949	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