Share Capital - Additional Information (Detail)	1 Months Ended				3 Months Ended	12 Months Ended
	Jan. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) shares	Jul. 31, 2020 USD ($) $ / shares shares	Aug. 31, 2019 USD ($)	Mar. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Mar. 31, 2021 SFr / shares	Dec. 31, 2020 SFr / shares	Aug. 31, 2019 SFr / shares
Class of Stock [Line Items]
Common stock, shares authorized | shares		115,172,786			115,172,786	115,172,786
Common shares, par value | SFr / shares							SFr 0.03	SFr 0.03
Proceeds from issuance of common shares					$ 214,592,000
July 2020 Offering [Member]
Class of Stock [Line Items]
Common shares sold | shares			7,400,000
Proceeds from issuance of common shares			$ 484,800,000
Common shares price per share | $ / shares			$ 70.00
Equity issuance costs			$ 32,500,000
Sales Agreement With Jefferies LLC [Member] | 2019 ATM [Member]
Class of Stock [Line Items]
Common shares, par value | SFr / shares									SFr 0.03
Common shares sold | shares						2,200,000
Average issue price of common shares | $ / shares						$ 89.47
Proceeds from issuance of common shares						$ 195,500,000
Equity issuance costs						$ 4,500,000
Sales Agreement With Jefferies LLC [Member] | 2020 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds	$ 46,700,000
Common shares sold | shares	300,000					1,800,000
Average issue price of common shares | $ / shares	$ 162.46					$ 169.57
Proceeds from issuance of common shares						$ 298,000,000.0
Equity issuance costs	$ 700,000					4,500,000
Payments of stamp taxes related to securities					500,000	4,900,000
Payable of stamp taxes related to securities		$ 4,000,000.0				$ 4,000,000.0
Sales Agreement With Jefferies LLC [Member] | 2021 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds					$ 177,800,000
Common shares sold | shares					1,100,000
Average issue price of common shares | $ / shares					$ 169.82
Equity issuance costs					$ 2,400,000
Payable of stamp taxes related to securities					$ 1,800,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2019 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds				$ 200,000,000.0
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2020 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds		$ 350,000,000.0
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2021 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds	$ 600,000,000.0