Combined Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Prepaid expenses and other current assets, related parties	$ 36	$ 19
Accounts payable, related parties	57	45
Accrued expenses, related parties	176	2
Accrued interest, related parties	483	13
Convertible promissory notes payable at fair value, related parties	21,103	1,950
Warrant liabilities, related parties	$ 106,925	$ 0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized shares	50,000,000
Common stock, issued shares	11,876,518
Common stock, outstanding shares	7,420,989	6,760,334