Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Series A Redeemable Convertible Preferred Stock [Member]	Series B Redeemable Convertible Preferred Stock [Member]	Series C Redeemable Convertible Preferred Stock [Member]	Series D Redeemable Convertible Preferred Stock [Member]	Series D-1 Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2013	$ 3,343	$ 3,313	$ 11,892			$ 18,548
Balance at Dec. 31, 2013							$ 1,438		$ (25,705)	$ (24,267)
Net loss									(24,455)	(24,455)
Stock-based compensation expense								$ 214		214
Change in par value							(1,438)	1,438
Conversion of 2013 convertible notes into Series D preferred stock				$ 4,159		4,159
Issuance of Series D preferred stock as financing fee				1,500		1,500
Balance at Dec. 31, 2014	3,343	3,313	11,892	5,659		24,207
Balance at Dec. 31, 2014								1,652	(50,160)	(48,508)
Net loss									(54,664)	(54,664)
Stock-based compensation expense								2,369		2,369
Balance at Dec. 31, 2015							1	94,702	(104,824)	(10,121)
Exercise of stock options and warrants								4,749		4,749
Issuance of Series D-1 preferred stock					$ 4,000	4,000
Issuance of common stock in connection with IPO, net of discounts and commissions							1	59,891		59,892
Conversion of 2013 warrants to equity classification								1,110		1,110
Conversion of preferred stock into common stock upon IPO	$ (3,343)	$ (3,313)	$ (11,892)	$ (5,659)	$ (4,000)	$ (28,207)		28,207		28,207
Offering expenses charged to equity								(3,276)		(3,276)
Net loss									(16,516)	(16,516)
Stock-based compensation expense								6,600		6,600
Balance at Dec. 31, 2016							$ 1	102,643	$ (121,340)	(18,696)
Exercise of stock options and warrants								896		896
Write-off of deferred offering costs								$ 445		$ 445