Equity - Additional Information (Detail) - USD ($)					1 Months Ended	3 Months Ended
Equity - Additional Information (Detail) - USD ($)	Mar. 20, 2024	Jan. 19, 2024	May 10, 2023	Feb. 13, 2023	Jul. 31, 2021	Mar. 31, 2024	Jan. 11, 2024	Dec. 31, 2023	Sep. 30, 2022	Apr. 30, 2022
Class Of Stock [Line Items]
Number of shares agreed to sell						84,865,021		79,700,262
Common stock, no par value						$ 0		$ 0
Common stock, voting rights description						Each common share entitles the holder to one vote on all matters submitted to a vote of the Company’s shareholders.
Cash dividends						$ 0
May 2023 Purchase Agreement [Member]
Class Of Stock [Line Items]
Number of shares agreed to sell			4,784,689
Purchase price per share			$ 4.18
Net proceeds of common shares			$ 20,000,000
Common stock, no par value			$ 0
February 2023 Purchase Agreement [Member]
Class Of Stock [Line Items]
Number of shares agreed to sell				17,648,596
Purchase price per share				$ 3.4
Net proceeds of common shares				$ 56,000,000
Common stock, no par value				$ 0
Open Market Sales Agreement [Member]
Class Of Stock [Line Items]
Net proceeds of common shares						$ 119,400,000
Number of common shares issued and sold						18,504,652
Open Market Sales Agreement [Member] \| Maximum [Member]
Class Of Stock [Line Items]
Net proceeds of common shares					$ 100,000,000
Compensation percentage of gross proceeds					3.00%
Loan Agreement with Oxford Finance LLC
Class Of Stock [Line Items]
Number of shares issuable upon exercise of outstanding warrants (in shares)							33,818		170,010	26,110
Weighted-average exercise price per share (in dollars per share)							$ 8.87		$ 2.94	$ 7.66
Percentage of initial funding							2.00%		2.00%	2.00%
Initial funded amount							$ 15,000,000		$ 25,000,000	$ 10,000,000
Common share warrants outstanding						33,818
Loan Agreement with Oxford Finance LLC \| Warrant
Class Of Stock [Line Items]
Common share warrants, exercised	196,120
Number of warrants being cancelled	33,184
Loan Agreement with Oxford Finance LLC \| Common Stock [Member]
Class Of Stock [Line Items]
Number of common stock shares issued	162,936
Sales Agreement with Jefferies LLC [Member] \| Common Stock [Member]
Class Of Stock [Line Items]
Increase in aggregate offering price		$ 100,000,000
Aggregate offering price		$ 200,000,000

Fusion Pharmaceuticals Inc. 10-Q