Background (Details) - USD ($)				12 Months Ended
	Sep. 13, 2016	Mar. 03, 2016	Feb. 10, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Offering
Net Proceeds from Initial Public Offering				$ 246,489,901
Accumulated deficit				141,562,324	$ 58,550,520
Cash and Cash Equivalents, at Carrying Value				$ 240,429,839	$ 62,251,860	$ 3,119,713
Class B-1 Preferred Stock
Public Offering
Shares issued (in shares)					1,011,721	809,385
Shares converted (in shares)			3,278,938
Class B-2 Preferred Stock
Public Offering
Shares converted (in shares)			326,557
Class C Preferred Stock
Public Offering
Shares issued (in shares)					1,102,945	1,135,084
Shares converted (in shares)			2,365,020
Net proceeds from issuance of common stock					$ 5,000,020	$ 4,500,034
Class D Preferred Stock
Public Offering
Shares issued (in shares)					3,093,092
Shares converted (in shares)			3,105,000
Net proceeds from issuance of common stock					$ 64,787,549
Common Stock | IPO
Public Offering
Shares issued (in shares)			4,750,000	5,277,941
Share price (in dollars per share)			$ 20.00
Net Proceeds from Initial Public Offering			$ 88,350,000
Shares converted (in shares)				8,695,640
Common Stock | Over-Allotment Option
Public Offering
Shares issued (in shares)	637,500	527,941
Share price (in dollars per share)		$ 20.00
Net Proceeds from Initial Public Offering		$ 9,800,000
Common Stock | Follow-On Offering
Public Offering
Number of common shares to be sold under public offering	4,887,500
Shares issued (in shares)	4,597,645
Share price (in dollars per share)	$ 34.50
Net proceeds from issuance of common stock	$ 149,100,000
Common Stock | Stock Sold by Selling Stockholder
Public Offering
Shares issued (in shares)	289,855