CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity, beginning of period at Dec. 31, 2018	$ 90,192	$ 3	$ 246,927	$ 439	$ (157,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		46,809
Issuance of common stock upon exercise of stock options, net of shares withheld	125		125
Stock-based compensation	1,871		1,871
Vesting of early exercised stock options	66		66
Additional accrual of IPO related costs	(160)		(160)
Foreign currency translation	(19)			(19)
Net unrealized gain (loss) on marketable securities	25			25
Net loss	(9,345)				(9,345)
Stockholders' equity, end of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity, end of period at Mar. 31, 2019	82,755	$ 3	248,829	445	(166,522)
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity, beginning of period at Dec. 31, 2018	$ 90,192	$ 3	246,927	439	(157,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock related to employee stock purchase plan (in shares)	99,086
Issuance of common stock related to employee stock purchase plan	$ 1,300
Foreign currency translation	(11)
Net unrealized gain (loss) on marketable securities	47
Net loss	(29,305)
Stockholders' equity, end of period (in shares) at Sep. 30, 2019		24,965,512
Stockholders' equity, end of period at Sep. 30, 2019	68,961	$ 3	254,965	475	(186,482)
Stockholders' equity, beginning of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity, beginning of period at Mar. 31, 2019	82,755	$ 3	248,829	445	(166,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		137,185
Issuance of common stock upon exercise of stock options, net of shares withheld	442		442
Issuance of common stock related to employee stock purchase plan (in shares)		99,086
Issuance of common stock related to employee stock purchase plan	1,263		1,263
Issuance of common stock upon vesting of restricted stock units (in shares)		27,320
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	1,814		1,814
Vesting of early exercised stock options	56		56
Foreign currency translation	12			12
Net unrealized gain (loss) on marketable securities	59			59
Net loss	(8,654)				(8,654)
Stockholders' equity, end of period (in shares) at Jun. 30, 2019		24,761,157
Stockholders' equity, end of period at Jun. 30, 2019	77,747	$ 3	252,404	516	(175,176)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		175,070
Issuance of common stock upon exercise of stock options, net of shares withheld	611		611
Issuance of common stock upon vesting of restricted stock units (in shares)		38,115
Issuance of common stock upon vesting of restricted stock units	0
Repurchase of unvested early exercised stock options (in shares)		(8,830)
Repurchase of unvested early exercised stock options	0
Stock-based compensation	1,911		1,911
Vesting of early exercised stock options	39		39
Foreign currency translation	(4)			(4)
Net unrealized gain (loss) on marketable securities	(37)			(37)
Net loss	(11,306)				(11,306)
Stockholders' equity, end of period (in shares) at Sep. 30, 2019		24,965,512
Stockholders' equity, end of period at Sep. 30, 2019	68,961	$ 3	254,965	475	(186,482)
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2019		25,163,803
Stockholders' equity, beginning of period at Dec. 31, 2019	63,008	$ 3	258,121	464	(195,580)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from public offering, net of underwriting discounts, commissions and offering costs (in shares)		3,135,053
Issuance of common stock from public offering, net of underwriting discounts, commissions and offering costs	62,978		62,978
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		43,334
Issuance of common stock upon exercise of stock options, net of shares withheld	174		174
Issuance of common stock upon vesting of restricted stock units (in shares)		63,938
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	2,622		2,622
Vesting of early exercised stock options	27		27
Foreign currency translation	12			12
Net unrealized gain (loss) on marketable securities	221			221
Net loss	(12,772)				(12,772)
Stockholders' equity, end of period (in shares) at Mar. 31, 2020		28,406,128
Stockholders' equity, end of period at Mar. 31, 2020	116,270	$ 3	323,922	697	(208,352)
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2019		25,163,803
Stockholders' equity, beginning of period at Dec. 31, 2019	$ 63,008	$ 3	258,121	464	(195,580)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)	227,334
Issuance of common stock related to employee stock purchase plan (in shares)	74,685
Issuance of common stock related to employee stock purchase plan	$ 1,000
Foreign currency translation	(23)
Net unrealized gain (loss) on marketable securities	(11)
Net loss	(34,718)
Stockholders' equity, end of period (in shares) at Sep. 30, 2020		28,838,577
Stockholders' equity, end of period at Sep. 30, 2020	102,031	$ 3	331,896	430	(230,298)
Stockholders' equity, beginning of period (in shares) at Mar. 31, 2020		28,406,128
Stockholders' equity, beginning of period at Mar. 31, 2020	116,270	$ 3	323,922	697	(208,352)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		46,608
Issuance of common stock upon exercise of stock options, net of shares withheld	185		185
Issuance of common stock related to employee stock purchase plan (in shares)		74,685
Issuance of common stock related to employee stock purchase plan	991		991
Issuance of common stock upon vesting of restricted stock units (in shares)		85,030
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	2,955		2,955
Vesting of early exercised stock options	26		26
Foreign currency translation	(2)			(2)
Net unrealized gain (loss) on marketable securities	(85)			(85)
Net loss	(12,472)				(12,472)
Stockholders' equity, end of period (in shares) at Jun. 30, 2020		28,612,451
Stockholders' equity, end of period at Jun. 30, 2020	107,868	$ 3	328,079	610	(220,824)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		137,392
Issuance of common stock upon exercise of stock options, net of shares withheld	628		628
Issuance of common stock upon vesting of restricted stock units (in shares)		88,734
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	3,180		3,180
Vesting of early exercised stock options	9		9
Foreign currency translation	(33)			(33)
Net unrealized gain (loss) on marketable securities	(147)			(147)
Net loss	(9,474)				(9,474)
Stockholders' equity, end of period (in shares) at Sep. 30, 2020		28,838,577
Stockholders' equity, end of period at Sep. 30, 2020	$ 102,031	$ 3	$ 331,896	$ 430	$ (230,298)