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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Period Type:

Employee compensation plans - Narrative (Details)			12 Months Ended
Employee compensation plans - Narrative (Details)	Feb. 06, 2026 shares	Jan. 09, 2026 shares	Dec. 31, 2025 USD ($) plan shares	Dec. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($)	Mar. 01, 2024 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employee compensation plans \| plan			2
Maximum annual contribution under defined contribution plan			$ 23,500	$ 23,000	$ 22,500
Employer contribution to defined contribution plan			6,800,000	4,900,000	4,400,000
Deferred bonus amounts			18,700,000
Minimum bonus and salary amount			$ 200,000
Vesting period			3 years
Bonus deferral credit, minimum salary and bonus amount			$ 500,000
Deferral of salary and bonus (as a percent)			50.00%
Elective deferral credit period one			5 years
Elective deferral credit period two			10 years
Elective deferral credit, amount vested (as a percent)			100.00%
Matching credit (as a percent)			10.00%
Deferred compensation plans cost			$ 32,600,000	38,700,000	33,600,000
Executive Deferred Compensation Plan and Deferred Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred bonus amounts			$ 12,900,000	12,100,000	10,100,000
Vesting period of deferred bonus			5 years
Executive Deferred Compensation Plan, Deferred Incentive Plan And Capital Markets Deferred Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's deferred compensation liability			$ 75,200,000
CIBC Deferred Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company's deferred compensation liability			25,200,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense relating to the share-based awards			$ 0	2,550,000	8,195,000
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			5 years
Aggregate intrinsic value of non-option awards			$ 65,800,000
Compensation expense relating to the share-based awards			$ 19,200,000	32,600,000	3,900,000
Weighted Average Remaining Contractual Life			3 years
Non-option equity instruments, unvested (in shares) \| shares			2,642,276
Liability related to the non-option equity awards			$ 49,300,000
Total unrecognized compensation cost			$ 29,500,000
Stock Appreciation Rights (SARs) \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		5 years
Granted (in shares) \| shares		374,380
Minimum \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Maximum \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			5 years
Class A Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available under the share-based compensation plans (in shares) \| shares			771,375			1,000,000
Class A Stock \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of non-option awards			$ 91,500,000
Compensation expense relating to the share-based awards			13,000,000.0	$ 12,900,000	$ 13,100,000
Unrecognized compensation cost related to unvested share-based compensation			$ 20,500,000
Weighted Average Remaining Contractual Life			1 year 4 months 24 days	1 year 7 months 6 days
Granted (in shares) \| shares			227,625
Vested (in shares) \| shares			340,491
Non-option equity instruments, unvested (in shares) \| shares			1,265,307	1,434,968
Class A Stock \| Restricted Stock \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Granted (in shares) \| shares	330,440
Class A Stock \| Restricted Stock \| Subsequent Event \| Third Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares	138,685
Class A Stock \| Restricted Stock \| Subsequent Event \| Fifth Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares) \| shares	191,755
Class A Stock \| Minimum \| Restricted Stock \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Class A Stock \| Maximum \| Restricted Stock \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years