Nature of the Business and Basis of Presentation - Stock Split & Public Offering (Details) $ / shares in Units, $ in Thousands			1 Months Ended			3 Months Ended
	May 11, 2017 USD ($) $ / shares shares	May 09, 2017 USD ($) $ / shares shares	May 31, 2017 USD ($)	Oct. 31, 2016	Feb. 29, 2016 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) $ / shares shares	Jul. 31, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($)	Apr. 30, 2017 shares	Apr. 21, 2017 shares	Dec. 31, 2016 $ / shares shares
Stock Split
Stock Split				500
Public Offering
Issuance of common shares | shares					429,000		1,090,500
Fair value of common share | $ / shares					$ 7.00		$ 7.70
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses			$ 176,367
Other offering expenses					$ 23	$ 2,049	$ 97	$ 23
Common stock, shares authorized | shares						38,000,000					38,000,000
Common stock, par value (in dollars per share) | $ / shares						$ 0					$ 0
Preferred stock, shares authorized | shares						11,242,172					11,242,172
Preferred stock, par value (in dollars per share) | $ / shares						$ 0					$ 0
Subsequent Event
Public Offering
Aggregate net proceeds from the IPO and underwriters issuance	$ 176,367
Common stock, shares authorized | shares	200,000,000								50,000,000	50,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0
Preferred stock, shares authorized | shares	10,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0
Subsequent Event | Initial public offering
Public Offering
Issuance of common shares | shares		9,900,000
Fair value of common share | $ / shares		$ 17.00
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses		$ 152,889
Underwriting discounts and commissions		11,781
Other offering expenses		$ 3,630
Convertible preferred stock converted into shares of common stock | shares		9,358,560
Subsequent Event | Over allotment option
Public Offering
Issuance of common shares | shares	1,485,000
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses	$ 23,478
Underwriting discounts and commissions	1,767
Aggregate net proceeds from the IPO and underwriters issuance	$ 176,367
Subsequent Event | Over allotment option | BMS and AstraZenca
Public Offering
Issuance of common shares | shares	1,883,523	1,883,523
Common shares value issued	$ 0