Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Common stock and Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Temporary equity, Beginning Balance at Dec. 31, 2017		$ 29,700
Temporary equity, Beginning Balance, Shares at Dec. 31, 2017		28,763,000
Beginning Balance at Dec. 31, 2017	$ (15,022)			$ 1,243		$ (16,265)
Beginning Balance, Shares at Dec. 31, 2017			1,550,000
Temporary equity, Issuance of convertible preferred stock		$ 63,275
Temporary equity, Issuance of convertible preferred stock, shares		19,641,000
Vesting of stock subject to repurchase	8			8
Vesting of stock subject to repurchase, shares			529,000
Exercise of stock options	171			171
Exercise of stock options, shares			265,000
Stock-based compensation	698			698
Net loss	(11,032)					(11,032)
Ending Balance at Jun. 30, 2018	(25,177)			2,120		(27,297)
Ending Balance, Shares at Jun. 30, 2018			2,344,000
Temporary equity, Ending Balance at Jun. 30, 2018		$ 92,975
Temporary equity, Ending Balance, Shares at Jun. 30, 2018		48,404,000
Temporary equity, Beginning Balance at Mar. 31, 2018		$ 92,975
Temporary equity, Beginning Balance, Shares at Mar. 31, 2018		48,404,000
Beginning Balance at Mar. 31, 2018	(19,976)			1,753		(21,729)
Beginning Balance, Shares at Mar. 31, 2018			2,191,000
Vesting of stock subject to repurchase	5			5
Vesting of stock subject to repurchase, shares			3,000
Exercise of stock options	91			91
Exercise of stock options, shares			150,000
Stock-based compensation	271			271
Net loss	(5,568)					(5,568)
Ending Balance at Jun. 30, 2018	(25,177)			2,120		(27,297)
Ending Balance, Shares at Jun. 30, 2018			2,344,000
Temporary equity, Ending Balance at Jun. 30, 2018		$ 92,975
Temporary equity, Ending Balance, Shares at Jun. 30, 2018		48,404,000
Beginning Balance at Dec. 31, 2018	160,225			203,544	$ 61	(43,380)
Beginning Balance, Shares at Dec. 31, 2018			24,061,000
Vesting of stock subject to repurchase	71			71
Vesting of stock subject to repurchase, shares			46,000
Exercise of stock options	$ 87			87
Exercise of stock options, shares	63,014		63,000
Issuance of stock under Stock Purchase Plan	$ 379			379
Issuance of stock under Stock Purchase Plan, shares			25,000
Stock-based compensation	2,609			2,609
Comprehensive income	173				173
Net loss	(21,443)					(21,443)
Ending Balance at Jun. 30, 2019	142,101			206,690	234	(64,823)
Ending Balance, Shares at Jun. 30, 2019			24,195,000
Beginning Balance at Mar. 31, 2019	152,394			204,645	145	(52,396)
Beginning Balance, Shares at Mar. 31, 2019			24,115,000
Vesting of stock subject to repurchase	18			18	0	0
Vesting of stock subject to repurchase, shares			13,000
Exercise of stock options	67			67	0	0
Exercise of stock options, shares			42,000
Issuance of stock under Stock Purchase Plan	379			379	0	0
Issuance of stock under Stock Purchase Plan, shares			25,000
Stock-based compensation	1,581		$ 0	1,581	0	0
Comprehensive income	89		0	0	89	0
Net loss	(12,427)		$ 0	0	0	(12,427)
Ending Balance at Jun. 30, 2019	$ 142,101			$ 206,690	$ 234	$ (64,823)
Ending Balance, Shares at Jun. 30, 2019			24,195,000