Nature of the Business and Basis of Presentation - Initial Public Offering (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		6 Months Ended
	Jun. 30, 2018	May 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Public Offering
Fair value of common share	$ 45.00		$ 45.00
Other offering expenses	$ 111		$ 2,987	$ 3,053
Shares issued on conversion of preferred stock		9,358,560
Aggregate net proceeds from the IPO and underwriters issuance		$ 176,128
IPO
Public Offering
Issuance of common shares		9,900,000
Fair value of common share		$ 17.00
Proceeds from issuance of common shares upon completion of initial public offering, net of underwriting commissions and discounts		$ 152,651
Underwriting discounts and commissions		11,781
Other offering expenses		$ 3,868
Over allotment option
Public Offering
Issuance of common shares		1,485,000
Proceeds from issuance of common shares upon completion of initial public offering, net of underwriting commissions and discounts		$ 23,478
Underwriting discounts and commissions		$ 1,767