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Investment Securities (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($) rental security	Dec. 31, 2024 USD ($)
Debt Securities, Available-for-sale [Line Items]
Number of positions | security	343
Number of securities which impairment considered insignificant | security	89
Available-for-sale securities, gross unrealized loss, considered insignificant | $	$ 0.8
Securities in unrealized loss position | $	289.9	$ 405.6
Accumulated gross unrealized gain (loss) | $	115.7
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Interest receivable | $	30.0	36.0
Securities pledged as collateral | $	$ 8,200.0	$ 7,900.0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Number of positions	7
U.S. Government agency and sponsored enterprise residential MBS
Debt Securities, Available-for-sale [Line Items]
Number of positions	55
U.S. Government agency and sponsored enterprise commercial MBS
Debt Securities, Available-for-sale [Line Items]
Number of positions	22
SBA securities
Debt Securities, Available-for-sale [Line Items]
Number of positions	17
Private label residential MBS and CMOs
Debt Securities, Available-for-sale [Line Items]
Number of positions	109
Percentage of weighted average collateral loss	2.30%
Percentage of weighted average credit support	18.30%
Percentage of securities rated AAA	96.00%
Percentage of securities rated AA	4.00%
Private label commercial MBS
Debt Securities, Available-for-sale [Line Items]
Number of positions	26
Percentage of weighted average collateral loss	7.10%
Percentage of weighted average credit support	46.70%
Percentage of securities rated AAA	90.00%
Percentage of securities rated AA	9.00%
Percentage of securities rated A	1.00%
Single family real estate-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of positions	6
Percentage of weighted average collateral loss	6.80%
Percentage of weighted average credit support	60.30%
Percentage of securities rated AAA	56.00%
Percentage of securities rated AA	44.00%
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Number of positions	5
Percentage of weighted average collateral loss	16.20%
Percentage of weighted average credit support	39.10%
Percentage of securities rated AAA	61.00%
Percentage of securities rated AA	39.00%
Non-mortgage asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Number of positions	3
Percentage of weighted average collateral loss	3.90%
Percentage of weighted average credit support	22.80%
State and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Number of positions	4

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