Common Shares- Other Info (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		3 Months Ended
	May 11, 2017	May 09, 2017	May 31, 2017	Feb. 29, 2016	Mar. 31, 2017	Jul. 31, 2016	Mar. 31, 2016	Apr. 30, 2017	Apr. 21, 2017	Dec. 31, 2016
Issuance of common shares				429,000		1,090,500
Issuance price per share				$ 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					38,000,000					38,000,000
Common stock, par value (in dollars per share)					$ 0					$ 0
Preferred stock, shares authorized					11,242,172					11,242,172
Preferred stock, par value (in dollars per share)					$ 0					$ 0
Subsequent Event
Aggregate net proceeds from the IPO and underwriters issuance	$ 176,367
Common stock, shares authorized	200,000,000							50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0
Preferred stock, shares authorized	10,000,000
Preferred stock, par value (in dollars per share)	$ 0
Subsequent Event | Initial public offering
Issuance of common shares		9,900,000
Issuance price per share		$ 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		9,358,560
Subsequent Event | Over allotment option
Issuance of common shares	1,485,000
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses	$ 23,478
Net proceeds from underwriting	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
Issuance of common shares	1,883,523	1,883,523
Common shares value issued	$ 0