Consolidated Statements of Stockholders' Equity (Deficit) (unaudited) - USD ($) $ in Thousands	Total	Series A Preferred Stock	Series A-1 Preferred Stock	Class A Common Stock	IPO	Common Stock	Common Stock IPO	Additional Paid-in Capital	Additional Paid-in Capital IPO	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2014	$ (5,327)	$ 3	$ 5	$ 1		$ 11		$ 62,203		$ (67,508)	$ (42)
Beginning Balance, shares at Dec. 31, 2014		3,129,084	5,225,879	1,164,105		11,237,257
Stock-based compensation	1,522							1,522
Stock-based compensation, shares						6,023
Repurchase of common stock	(1,500)							(1,500)
Repurchase of common stock, shares						(173,913)
Exercise of stock options	$ 49							49
Exercise of stock options, shares	37,559					37,559
Other comprehensive income (loss)	$ 29										29
Net loss	(10,824)									(10,824)
Ending Balance at Dec. 31, 2015	(16,051)	$ 3	$ 5	$ 1		$ 11		62,274		(78,332)	(13)
Ending Balance, shares at Dec. 31, 2015		3,129,084	5,225,879	1,164,105		11,106,926
Stock-based compensation	2,165							2,165
Issuance of common stock in initial public offering, net of issuance costs					$ 66,102		$ 6		$ 66,096
Issuance of common stock in initial public 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 warrant, shares						100,683
Exercise of stock options	$ 748					$ 1		747
Exercise of stock options, shares	161,336					161,336
Exercise of warrant	$ 25							25
Exercise of warrant, shares						10,029
Other comprehensive income (loss)	(300)										(300)
Net loss	(8,658)									(8,658)
Ending Balance at Sep. 30, 2016	$ 44,031					$ 27		$ 131,307		$ (86,990)	$ (313)
Ending Balance, shares at Sep. 30, 2016						27,148,042