Derivative financial instruments - Information about Fair Values of Derivative Instruments in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2026	Dec. 31, 2025
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	$ 217,000	$ 245,000
Subject to master netting agreements	425,000	454,000
Reduction in estimated fair value of interest rate contracts in asset position	(362,000)	(341,000)
Reduction in estimated fair value of interest rate contracts in liability position	(15,000)	(32,000)
Fair value hedges:
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	159,000	190,000
Subject to master netting agreements	415,000	409,000
Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	29,000	1,000
Subject to master netting agreements	1,000	16,000
Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	29,000	54,000
Subject to master netting agreements	9,000	29,000
Interest rate swap agreements \| Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	12,000	0
Subject to master netting agreements	0	15,000
Commitments to sell real estate loans \| Fair value hedges: \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	17,000	1,000
Subject to master netting agreements	1,000	1,000
Commitments to sell real estate loans \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	11,000	24,000
Subject to master netting agreements	2,000	6,000
Commitments to originate real estate loans for sale \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	9,000	17,000
Subject to master netting agreements	3,000	21,000
Interest Rate Contract For Real Estate Loans \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	9,000	13,000
Subject to master netting agreements	4,000	2,000
Interest Rate Contracts \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	140,000	173,000
Subject to master netting agreements	398,000	394,000
Foreign exchange and other option and futures contracts \| Fair value hedges: \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Subject to master netting agreements	19,000	17,000
Subject to master netting agreements	$ 17,000	$ 15,000

Increase (decrease) in estimated fair value of interest rate contracts in asset position.

No definition available.

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- Definition

Increase (decrease) in estimated fair value of interest rate contracts in liability position.

+ References

No definition available.

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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