CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Conversion of convertible preferred stock to Class B common stock	Common Class A	Common Class B	Convertible Preferred Shares	Common Stock Common Class A	Common Stock Common Class A Conversion of Class B common stock to Class A common stock	Common Stock Common Class B	Common Stock Common Class B Conversion of convertible preferred stock to Class B common stock	Common Stock Common Class B Conversion of Class B common stock to Class A common stock	Additional Paid-in Capital	Additional Paid-in Capital Conversion of convertible preferred stock to Class B common stock	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Convertible Preferred Stock, beginning balance (in shares) at Dec. 31, 2016					43,109,054
Convertible Preferred Stock, beginning balance at Dec. 31, 2016					$ 129,842
Increase (Decrease) in Temporary Equity [Roll Forward]
Exercise of stock options					$ 49,863
Issuance of stock (in shares)					6,609,030
Convertible Preferred Stock, ending balance (in shares) at Dec. 31, 2017					49,718,084
Convertible Preferred Stock, ending balance at Dec. 31, 2017					$ 179,705
Beginning balance (in shares) at Dec. 31, 2016						0		23,000,900
Beginning balance at Dec. 31, 2016	$ (78,249)					$ 0		$ 1			$ 6,709		$ (2,109)	$ (49)	$ (82,801)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	414,000							412,163
Exercise of stock options	$ 611										611
Vesting of early exercised stock options (in shares)								461,011
Vesting of early exercised stock options	248										248
Issuance of common stock under (ESPP in shares)						0
Stock-based compensation	2,793										2,793
Vesting of restricted stock units (in shares)								5,000
Vesting of restricted stock units	16										16
Net loss	(32,450)														(32,450)
Other comprehensive income (loss)	25													25
Ending balance at Dec. 31, 2017	(107,006)					$ 0		$ 1			10,377		(2,109)	(24)	(115,251)
Ending balance (in shares) at Dec. 31, 2017						0		23,879,074
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of change in accounting policy	$ 0
Issuance of stock (in shares)					3,912,129
Issuance of stock					$ 39,879
Convertible Preferred Stock, ending balance (in shares) at Dec. 31, 2018	53,630,213				53,630,213
Convertible Preferred Stock, ending balance at Dec. 31, 2018	$ 219,584				$ 219,584
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,264,000							1,005,839
Exercise of stock options	$ 1,561										1,561
Vesting of early exercised stock options (in shares)								119,737
Vesting of early exercised stock options	337										337
Issuance of common stock under (ESPP in shares)						0
Stock-based compensation	4,079										4,079
Repayment of stockholder note (in shares)								21,186
Repayment of stockholder note	50										50
Net loss	(30,935)														(30,935)
Other comprehensive income (loss)	(12)													(12)
Ending balance at Dec. 31, 2018	(131,927)					$ 0		$ 1			16,403		(2,109)	(36)	(146,186)
Ending balance (in shares) at Dec. 31, 2018						0		25,025,836
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of change in accounting policy	$ 0
Conversion of convertible preferred stock to Class B common stock (in shares)					(53,630,213)
Conversion of convertible preferred stock to Class B common stock					$ (219,584)
Convertible Preferred Stock, ending balance (in shares) at Dec. 31, 2019	0				0
Convertible Preferred Stock, ending balance at Dec. 31, 2019	$ 0				$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of stock (in shares)				53,600,000			46,422,400		53,630,213	46,422,400
Conversion of stock		$ 219,584					$ 1		$ 1	$ (1)		$ 219,583
Conversion of convertible preferred stock warrants into Class B common stock warrants	5,665										5,665
Issuance of Class A common stock in connection with the IPO, net of underwriting discounts (in shares)			12,900,000			12,937,500
Issuance of Class A common stock in connection with the IPO, net of underwriting discounts	$ 186,912										186,912
Exercise of stock options (in shares)	2,650,000					1,289,600		1,211,230
Exercise of stock options	$ 5,579										5,579
Exercise of common stock warrants (in shares)								224,102
Vesting of early exercised stock options (in shares)								162,101
Vesting of early exercised stock options	620										620
Issuance of common stock under (ESPP in shares)						305,194
Issuance of common stock under ESPP	4,150										4,150
Stock-based compensation	12,586										12,586
Repayment of stockholder note (in shares)								31,939
Repayment of stockholder note	74										74
Retirement of treasury stock											(2,109)		2,109
Net loss	(51,550)														(51,550)
Other comprehensive income (loss)	232													232
Ending balance at Dec. 31, 2019	257,652					$ 1		$ 1			$ 449,463		$ 0	$ 196	$ (192,009)
Ending balance (in shares) at Dec. 31, 2019						60,954,694		33,863,021
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of change in accounting policy	$ 5,727