Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total		Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2017	$ (72,328)				$ 948	$ (73,234)	$ (42)
Balance, shares at Dec. 31, 2017			30,459,574
Balance at Dec. 31, 2017			$ 226,196
Balance, shares at Dec. 31, 2017				3,278,129
Conversion of preferred stock to common stock	226,198			$ 3	226,195
Conversion of preferred stock to common stock, shares			(30,459,574)
Conversion of preferred stock to common stock			$ (226,196)
Conversion of preferred stock to common stock, shares				30,459,574
Issuance of common stock upon IPO	124,716			$ 1	124,715
Issuance of common stock upon IPO, shares				9,200,000
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares	$ 80				80
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares	708,760			60,524
Vesting of early exercised stock options and restricted stock	$ 278				278
Vesting of early exercised stock options and restricted stock, shares				129,152
Stock-based compensation	656				656
Other comprehensive income (loss)	(55)						(55)
Net loss	(12,954)					(12,954)
Balance at Mar. 31, 2018	266,591			$ 4	352,872	(86,188)	(97)
Balance, shares at Mar. 31, 2018				43,127,379
Balance at Dec. 31, 2018	$ 234,942	[1]		$ 4	357,873	(122,828)	(107)
Balance, shares at Dec. 31, 2018	44,537,946			43,610,823
Cumulative effect adjustment upon adoption of ASC 606 | ASC 606	$ 2,212					2,212
Issuance of common stock upon exercise of stock options, net of amounts related to unvested shares, shares	69			69
Vesting of early exercised stock options and restricted stock	$ 273				273
Vesting of early exercised stock options and restricted stock, shares				114,934
Stock-based compensation	1,674				1,674
Other comprehensive income (loss)	136						136
Net loss	(17,670)					(17,670)
Balance at Mar. 31, 2019	$ 221,567			$ 4	$ 359,820	$ (138,286)	$ 29
Balance, shares at Mar. 31, 2019	44,534,594			43,725,826

[1] The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.