Statements of convertible preferred stock and preferred units, and stockholders' and members' equity (deficit) - USD ($) $ in Thousands	Total	Class A Units [Member]	Common Stock [Member]	Additional paid in capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]	Series A Convertible Preferred Stock [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Series D Convertible Preferred Stock [Member]	Convertible Preferred Stock And Preferred Units [Member]
Balances at Dec. 31, 2013							$ 3,779	$ 7,999					$ 11,778
Balances (Shares) at Dec. 31, 2013							119,656,000	95,315,000
Balances at Dec. 31, 2013	$ (13,921)	$ 10,885				$ (24,806)
Balances (Shares) at Dec. 31, 2013		132,148,000
Conversion from LLC to C corporation, Shares		(132,148,000)	2,643,000				(119,656,000)	(95,315,000)	2,393,000	1,906,000
Conversion from LLC to C corporation		$ (10,885)		$ 10,885			$ (3,779)	$ (7,999)	$ 3,779	$ 7,999
Accretion of preferred units	(815)			(815)					184	631			815
Discount on Related Party Promissory Notes	128			128
Exercise of stock options, Shares			2,000
Exercise of stock options	1			1
Stock-based compensation expense	319			319
Net loss	(4,003)					(4,003)
Balances at Dec. 31, 2014									$ 3,963	$ 8,630			12,593
Balances (Shares) at Dec. 31, 2014									2,393,000	1,906,000
Balances at Dec. 31, 2014	(18,291)			10,518		(28,809)
Balances (Shares) at Dec. 31, 2014			2,645,000
Issuance of convertible preferred stock, shares			7,245,000								4,047,000	7,367,000
Issuance of convertible preferred stock, net of transaction costs	145,184		$ 1	145,183							$ 26,021		26,021
Issuance of convertible preferred stock for the conversion of outstanding related party debt, Shares											585,000
Issuance of convertible preferred stock for the conversion of outstanding related party debt											$ 3,792		3,792
Issuance of convertible preferred stock, net of transaction costs												$ 67,998	67,998
Loss (gain) on extinguishment of convertible preferred stock	759			759					$ 1,317	$ (2,076)			(759)
Accretion of preferred units	(1,747)			(1,747)					$ (2,280)	$ 1,338	$ 187	$ 2,502	1,747
Conversion of convertible preferred stock into common stock upon initial public offering, Shares			16,298,000						(2,393,000)	(1,906,000)	(4,632,000)	(7,367,000)
Conversion of convertible preferred stock into common stock upon initial public offering	111,392		$ 2	111,390					$ (3,000)	$ (7,892)	$ (30,000)	$ (70,500)	$ (111,392)
Discount on Related Party Promissory Notes	13			13
Exercise of stock options, Shares			125,000
Exercise of stock options	107			107
Stock-based compensation expense	2,921			2,921
Unrealized (loss) gain on available-for-sale securities, net of income tax expense	(719)				$ (719)
Net loss	$ (22,811)					(22,811)
Balances (Shares) at Dec. 31, 2015	0
Balances at Dec. 31, 2015	$ 216,808		$ 3	269,144	(719)	(51,620)
Balances (Shares) at Dec. 31, 2015			26,313,000
Exercise of stock options, Shares			163,000
Exercise of stock options	179			179
Stock-based compensation expense	7,031			7,031
Unrealized (loss) gain on available-for-sale securities, net of income tax expense	686				686
Net loss	$ (62,967)					(62,967)
Balances (Shares) at Dec. 31, 2016	0
Balances at Dec. 31, 2016	$ 161,737		$ 3	$ 276,354	$ (33)	$ (114,587)
Balances (Shares) at Dec. 31, 2016			26,477,000