Fair Values of Financial Instruments - Schedule of Roll Forward of Level 3 Available-For-Sale Securities (Details) - State and local housing finance agency obligations - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of the period	$ 1,666,174	$ 1,445,172	$ 1,664,523	$ 1,297,431
Net unrealized gains (losses)	984	504	3,680	1,830
Purchases	0	0	0	150,000
Settlements	0	0	(1,045)	(3,585)
Balance, end of the period	$ 1,667,158	$ 1,445,676	$ 1,667,158	$ 1,445,676

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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