Consolidated Statements of Convertible Preferred Stock, Contingently Redeemable Common Stock and Stockholders’ (Deficit) Equity - USD ($) shares in Thousands, $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Series B-1 Convertible Preferred Stock	Contingently Redeemable Common Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2016		47,000	24,779	10,448
Beginning balance at Dec. 31, 2016		$ 47,112	$ 55,849	$ 36,077	$ 1,921
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)		(47,000)	(24,779)	(10,448)		22,284
Conversion of convertible preferred stock into common stock upon closing of initial public offering	$ 139,038	$ (47,112)	$ (55,849)	$ (36,077)		$ 23	$ 139,015
Reclassification of restricted stock awards upon termination of put option	2,191				(2,191)		2,191
Stock-based compensation expense	4,505				270		4,505
Ending balance (in shares) at Dec. 31, 2017		0	0	0
Ending balance at Dec. 31, 2017		$ 0	$ 0	$ 0	0
Beginning balance, common stock (in shares) at Dec. 31, 2016						2,424
Beginning balance at Dec. 31, 2016	(69,088)					$ 2	4,515	$ (433)	$ (73,172)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (in shares)						7,320
Issuance of stock	106,388					$ 7	106,381
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)		(47,000)	(24,779)	(10,448)		22,284
Conversion of convertible preferred stock into common stock upon closing of initial public offering	139,038	$ (47,112)	$ (55,849)	$ (36,077)		$ 23	139,015
Reclassification of restricted stock awards upon termination of put option	2,191				(2,191)		2,191
Exercise of common stock options (in shares)						144
Exercise of common stock options	462						462
Vesting of restricted stock awards (in shares)						77
Vesting of restricted stock awards	32						32
Stock-based compensation expense	4,505				270		4,505
Other comprehensive income	24							24
Net loss	$ (16,443)								(16,443)
Ending balance, common stock (in shares) at Dec. 31, 2017	32,249					32,249
Ending balance at Dec. 31, 2017	$ 167,109					$ 32	257,101	(409)	(89,615)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment upon adoption of ASC 606	(46,913)								(46,913)
Stock-based compensation expense	$ 9,407						9,407
Ending balance (in shares) at Dec. 31, 2018		0	0	0
Ending balance at Dec. 31, 2018		$ 0	$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	683
Exercise of common stock options	$ 1,546					$ 1	1,545
Vesting of restricted stock awards (in shares)						9
Vesting of restricted stock awards	28						28
Stock-based compensation expense	9,407						9,407
Other comprehensive income	331							331
Net loss	$ (27,379)								(27,379)
Ending balance, common stock (in shares) at Dec. 31, 2018	32,941					32,941
Ending balance at Dec. 31, 2018	$ 104,129					$ 33	$ 268,081	$ (78)	$ (163,907)