Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Series A Preferred Stock	Series A-1 Preferred Stock	Class A Common Stock	Common Stock	Common Stock IPO	Additional Paid-in Capital	Additional Paid-in Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2015	$ (16,051)		$ 3	$ 5	$ 1	$ 11		$ 62,274		$ (78,332)	$ (13)
Balance, shares at Dec. 31, 2015			3,129,084	5,225,879	1,164,105	11,106,926
Stock-based compensation	3,101							3,101
Issuance of common stock in offering, net of issuance costs		$ 66,103					$ 6		$ 66,097
Issuance of common stock in offering, net of issuance costs, shares							6,250,000
Conversion of convertible preferred stock and Class A common stock into common stock			$ (3)	$ (5)	$ (1)	$ 9
Conversion of convertible preferred stock and Class A common stock into common stock, shares			(3,129,084)	(5,225,879)	(1,164,105)	9,519,068
Cashless exercise of common stock warrant, shares						100,683
Exercise of stock options	750					$ 1		749
Exercise of stock options, shares						163,968
Exercise of common stock warrant	25							25
Exercise of common stock warrant, shares						10,029
Other comprehensive income (loss)	(290)										(290)
Net loss	(11,286)									(11,286)
Balance at Dec. 31, 2016	42,352					$ 27		132,246		(89,618)	(303)
Balance, shares at Dec. 31, 2016						27,150,674
Stock-based compensation	9,299							9,299
Issuance of common stock in offering, net of issuance costs	9,870					$ 1		9,869
Issuance of common stock in offering, net of issuance costs, shares						553,825
Purchase of convertible note capped call hedge	(12,922)							(12,922)
Equity component of convertible notes	22,094							22,094
Exercise of stock options	$ 2,869							2,869
Exercise of stock options, shares	497,175					497,175
Issuance of shares under employee stock purchase plan	$ 1,540							1,540
Issuance of shares under employee stock purchase plan, shares						128,786
Other comprehensive income (loss)	523										523
Net loss	(19,634)									(19,634)
Balance at Dec. 31, 2017	55,991					$ 28		164,995		(109,252)	220
Balance, shares at Dec. 31, 2017						28,330,460
Cumulative effect of adoption of ASU 2014-09, net of taxes	9,097									9,097
Stock-based compensation	25,825							25,825
Vesting of restricted stock units	1					$ 1
Vesting of restricted stock units, shares						671,412
Restricted stock units withheld to settle employee tax withholding liability	(7,925)							(7,925)
Restricted stock units withheld to settle employee tax withholding liability, shares						(154,567)
Exercise of stock options	$ 10,149					$ 1		10,148
Exercise of stock options, shares	778,370					778,370
Issuance of shares under employee stock purchase plan	$ 1,823							1,823
Issuance of shares under employee stock purchase plan, shares						74,517
Other comprehensive income (loss)	(5,288)										(5,288)
Net loss	(47,515)									(47,515)
Balance at Dec. 31, 2018	$ 42,158					$ 30		$ 194,866		$ (147,670)	$ (5,068)
Balance, shares at Dec. 31, 2018						29,700,192