Share Capital - Additional Information (Detail)	1 Months Ended						12 Months Ended
	Nov. 30, 2019 USD ($) $ / shares shares	Aug. 31, 2019 USD ($)	Sep. 30, 2018 USD ($) $ / shares shares	Aug. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) $ / shares shares	Oct. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2019 SFr / shares shares	Dec. 31, 2018 SFr / shares shares
Class of Stock [Line Items]
Common stock, shares authorized | shares									103,901,006	90,343,803
Common shares, par value | SFr / shares									SFr 0.03	SFr 0.03
Capital reserved for future issuance | shares									1,230,729
Proceeds from issuance of common shares							$ 415,019,000	$ 307,053,000
Common Stock, Voting Rights							one vote for each Common Share
Dividends declared and paid							$ 0
IPO [Member]
Class of Stock [Line Items]
Common shares sold | shares						4,400,000
Common shares price per share | $ / shares						$ 14.00
Proceeds from issuance of common shares						$ 53,700,000
Equity issuance costs						$ 8,300,000
Private Placement [Member] | Bayer Global Investments B.V [Member]
Class of Stock [Line Items]
Common shares sold | shares						2,500,000
Common shares price per share | $ / shares						$ 14.00
Proceeds from issuance of common shares						$ 35,000,000.0
Underwritten Public Offering [Member]
Class of Stock [Line Items]
Common shares sold | shares			4,200,000		5,700,000
Common shares price per share | $ / shares			$ 47.50		$ 22.75
Proceeds from issuance of common shares			$ 184,500,000		$ 122,600,000
Equity issuance costs			$ 15,500,000		$ 8,200,000
Underwritten Public Offering [Member] | Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold | shares	4,900,000
Common shares price per share | $ / shares	$ 64.50
Proceeds from issuance of common shares	$ 294,400,000
Equity issuance costs	$ 20,700,000
2018 ATM [Member] | Sales Agreement With Jefferies LLC [Member]
Class of Stock [Line Items]
Common shares sold | shares							2,800,000
Proceeds from issuance of common shares							$ 120,600,000
Equity issuance costs							$ 4,400,000
Average issue price of common shares | $ / shares							$ 44.38
2018 ATM [Member] | Sales Agreement With Jefferies LLC [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds				$ 125,000,000.0
2019 ATM [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds		$ 200,000,000.0