Organization and Operations - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Oct. 31, 2016	Oct. 31, 2016	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Mar. 31, 2015	Mar. 24, 2015
Organization and operations [Line Items]
Company formation date			Oct. 28, 2013
Company formation country name			Basel, Switzerland
Accumulated deficit			$ (57,083)		$ (33,906)
Proceeds from issuance of common shares			54,061
Proceeds from issuance of common shares in private placement			35,000
Common shares acquired	170,689
Cash	$ 315,500	$ 315,500	315,520		$ 155,961
Bayer Global Investments B.V [Member]
Organization and operations [Line Items]
Proceeds from issuance of common shares in private placement		$ 35,000	$ 35,000
IPO [Member]
Organization and operations [Line Items]
Issuance of shares, net of issuance cost (in shares)	4,429,311	4,429,311
Common shares price per share	$ 14.00	$ 14.00
Proceeds from issuance of common shares		$ 53,700
Common shares acquired		170,689
Overallotment Option [Member]
Organization and operations [Line Items]
Issuance of shares, net of issuance cost (in shares)	429,311	429,311
Common shares price per share	$ 14.00	$ 14.00
Common shares acquired		170,689
Concurrent Private Placement [Member] | Bayer Global Investments B.V [Member]
Organization and operations [Line Items]
Issuance of shares, net of issuance cost (in shares)	2,500,000	2,500,000	2,500,000
Common shares price per share	$ 14.00	$ 14.00
TRACR Hematology Limited [Member]
Organization and operations [Line Items]
Formation date, VIE			Jan. 23, 2014
Relationship nature and extent of involvement in VIE			On January 23, 2014, the founders of the Company formed TRACR Hematology Limited (“TRACR”) in the United Kingdom, to further the development of the CRISPR/Cas9 technology into medicines for the treatment of blood-borne illnesses. As the Company was funding and managing TRACR’s operations in 2014, it has been consolidated by the Company from the date that the Company established a variable interest in TRACR in April 2014. In March 2015, the Company acquired 82.1% of the outstanding equity of TRACR in a share exchange transaction. Concurrent with its initial public offering (“IPO”) in October 2016, the Company acquired the outstanding non-controlling interest in TRACR as such, as of December 31, 2016 TRACR is a wholly-owned subsidiary of the Company.
Purpose of VIE			To further the development of the CRISPR/Cas9 technology into medicines for the treatment of blood-borne illnesses.
Percentage of outstanding equity acquired			82.10%	82.10%		82.10%	82.10%