CONDENSED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Other prepaids and current assets, related parties, current	$ 0	$ 28
Operating sublease right-of-use asset, related party	2,013	0
Accrued liabilities, related parties, current	274	123
Lease liabilities, related parties, current	151	0
Lease liabilities, related parties, noncurrent	1,974	0
Deferred rent, related parties, noncurrent	$ 0	$ 72
Common stock, par or stated value per share	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares, issued	32,263,757	32,103,953
Common stock, shares, outstanding	31,711,124	31,394,830