Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity/(Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Redeemable convertible preferred stock beginning balance (in shares) at Dec. 31, 2016	55,422,002
Redeemable convertible preferred stock beginning balance at Dec. 31, 2016	$ 655,416
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 175,915
Conversion of redeemable convertible preferred stock to common stock (in shares)	(55,422,002)
Conversion of redeemable convertible preferred stock to common stock	$ (831,331)
Redeemable convertible preferred stock ending balance (in shares) at Dec. 31, 2017	0
Redeemable convertible preferred stock ending balance at Dec. 31, 2017	$ 0
Balance, beginning of period (in shares) at Dec. 31, 2016		14,687,024
Balance, beginning of period at Dec. 31, 2016	(563,734)	$ 15	$ 0	$ (563,749)	$ 0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock, net (in shares)		10,615,650
Issuance of common stock related to initial public offering, net	148,088	$ 10	148,078
Initial public offering costs	(3,708)		(3,708)
Issuance of common stock pursuant to exercise of stock options (in shares)		744,215
Issuance of common stock pursuant to exercise of stock options	3,001	$ 1	3,000
Stock-based compensation	11,369		11,369
Accretion of redeemable convertible preferred stock	(175,915)		(8,690)	(167,225)
Conversion of redeemable convertible preferred stock to common stock (in shares)		55,422,002
Conversion of redeemable convertible preferred stock to common stock	831,331	$ 55	213,781	617,495
Net loss	(15,002)			(15,002)
Balance, end of period (in shares) at Dec. 31, 2017		81,468,891
Balance, end of period at Dec. 31, 2017	$ 235,430	$ 81	364,352	(129,003)	0
Redeemable convertible preferred stock ending balance (in shares) at Dec. 31, 2018	0
Redeemable convertible preferred stock ending balance at Dec. 31, 2018	$ 0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock pursuant to employee stock purchase plan (in shares)		425,228
Issuance of common stock pursuant to employee stock purchase plan	6,588	$ 1	6,587
Issuance of common stock, net (in shares)		4,836,336
Issuance of common stock related to initial public offering, net	107,593	$ 5	107,588
Issuance of common stock pursuant to exercise of stock options (in shares)		3,203,528
Issuance of common stock pursuant to exercise of stock options	16,820	$ 3	16,817
Issuance of common stock pursuant to settlement restricted stock units (in shares)		306,079
Issuance of common stock pursuant to settlement of restricted stock units	0
Common stock surrendered for employees' tax liability upon settlement of restricted stock units (in shares)		(88,721)
Common stock surrendered for employees' tax liability upon settlement of restricted stock units	(1,426)		(1,426)
Equity component of convertible senior notes, net	27,951		27,951
Stock-based compensation	20,960		20,960
Net loss	$ (41,978)			(41,978)
Balance, end of period (in shares) at Dec. 31, 2018	90,151,341	90,151,341
Balance, end of period at Dec. 31, 2018	$ 371,938	$ 90	542,829	(170,981)	0
Redeemable convertible preferred stock ending balance (in shares) at Dec. 31, 2019	0
Redeemable convertible preferred stock ending balance at Dec. 31, 2019	$ 0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock pursuant to employee stock purchase plan (in shares)		490,717
Issuance of common stock pursuant to employee stock purchase plan	$ 6,732		6,732
Issuance of common stock pursuant to exercise of stock options (in shares)	1,666,162	1,666,162
Issuance of common stock pursuant to exercise of stock options	$ 9,570	$ 2	9,568
Issuance of common stock pursuant to settlement restricted stock units (in shares)		966,037
Issuance of common stock pursuant to settlement of restricted stock units	0	$ 1	(1)
Common stock surrendered for employees' tax liability upon settlement of restricted stock units (in shares)		(272,660)
Common stock surrendered for employees' tax liability upon settlement of restricted stock units	(5,126)		(5,126)
Stock-based compensation	29,095		29,095
Other comprehensive income (loss)	42				42
Net loss	$ (80,805)			(80,805)
Balance, end of period (in shares) at Dec. 31, 2019	93,001,597	93,001,597
Balance, end of period at Dec. 31, 2019	$ 331,446	$ 93	$ 583,097	$ (251,786)	$ 42