Share Capital - Additional Information (Detail)	1 Months Ended		3 Months Ended	9 Months Ended
	Aug. 31, 2019 USD ($)	Aug. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 SFr / shares	Dec. 31, 2018 SFr / shares shares
Class of Stock [Line Items]
Common stock, shares authorized			55,677,088	55,677,088			52,183,139
Common shares, par value | SFr / shares						SFr 0.03	SFr 0.03
Treasury stock, shares			256,989	256,989			307,936
Capital reserved for future issuance			230,729	230,729
Conditional capital reserved for future issuance			23,948,128	23,948,128			20,498,996
Net cash proceeds from sale of common stock | $				$ 121,216,000	$ 309,019,000
Sales Agreement With Jefferies LLC [Member] | 2018 ATM [Member]
Class of Stock [Line Items]
Common shares sold			1,452,880	2,816,568
Net cash proceeds from sale of common stock | $			$ 69,400,000	$ 121,900,000
Issuance costs | $			1,500,000	3,100,000
Payments of stamp taxes related to securities | $			500,000	700,000
Accrued stamp taxes | $			$ 700,000	$ 700,000
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2018 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds | $		$ 125,000,000.0
Sales Agreement With Jefferies LLC [Member] | Maximum [Member] | 2019 ATM [Member]
Class of Stock [Line Items]
Aggregate estimated gross proceeds | $	$ 200,000,000.0
Swiss Law [Member]
Class of Stock [Line Items]
Common stock, shares authorized			25,134,003	25,134,003
Debt Instruments [Member]
Class of Stock [Line Items]
Conditional capital reserved for future issuance			4,919,700	4,919,700
Employee Benefit Plans [Member]
Class of Stock [Line Items]
Conditional capital reserved for future issuance			19,028,428	19,028,428