Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Detail) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 97,431	$ 88,337
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(50,450)	(12,302)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	(46,365)	(69,691)
Net Amount, Derivatives, Financial Assets	616	6,344
Net Amount Recognized, Resell agreements, Financial Assets	0	9,650
Gross Amounts Not Offset Financial Instruments, Resell Agreements	0	0
Gross Amounts Not Offset Collateral, Resell Agreements, Financial Assets	0	(9,650)
Net Amount, Financial Assets, Resell Agreements	0	0
Net Amount Recognized, Total Financial Assets	97,431	97,987
Gross Amounts Not Offset Collateral, Financial Assets	(46,365)	(79,341)
Net Amount, Financial Assets	616	6,344
Net Amount Recognized, Derivatives, Financial Liabilities	148,885	22,504
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(50,450)	(12,302)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(90,974)	(10,181)
Net Amount, Derivatives, Financial Liabilities	7,461	21
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	5,116,888	4,525,855
Gross Amounts Not Offset Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset Collateral, Repurchase Agreements, Financial Liabilities	(5,116,888)	(4,525,855)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Total Financial Liabilities	5,265,773	4,548,359
Gross Amounts Not Offset Collateral, Financial Liabilities	(5,207,862)	(4,536,036)
Net Amount, Financial Liabilities	7,461	21
Counterparty H
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	22,822	35,230
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(22,822)	(907)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	(31,270)
Net Amount, Derivatives, Financial Assets	0	3,053
Net Amount Recognized, Derivatives, Financial Liabilities	64,763	907
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(22,822)	(907)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(39,120)	0
Net Amount, Derivatives, Financial Liabilities	2,821	0
Counterparty F
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	10,042	20,242
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(10,042)	(290)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	(19,495)
Net Amount, Derivatives, Financial Assets	0	457
Net Amount Recognized, Derivatives, Financial Liabilities	17,907	290
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(10,042)	(290)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(6,704)	0
Net Amount, Derivatives, Financial Liabilities	1,161	0
Counterparty B
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	8,773	13,619
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(8,773)	(1,184)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	(10,789)
Net Amount, Derivatives, Financial Assets	0	1,646
Net Amount Recognized, Derivatives, Financial Liabilities	29,708	1,184
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(8,773)	(1,184)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(19,820)	0
Net Amount, Derivatives, Financial Liabilities	1,115	0
Counterparty E
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	26,958	7,298
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(754)	(6,418)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	(25,990)	(220)
Net Amount, Derivatives, Financial Assets	214	660
Net Amount Recognized, Derivatives, Financial Liabilities	754	6,418
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(754)	(6,418)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	0	0
Net Amount, Derivatives, Financial Liabilities	0	0
Other counterparties
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	28,836	11,948
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(8,059)	(3,503)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	(20,375)	(7,917)
Net Amount, Derivatives, Financial Assets	402	528
Net Amount Recognized, Derivatives, Financial Liabilities	35,753	13,705
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(8,059)	(3,503)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(25,330)	(10,181)
Net Amount, Derivatives, Financial Liabilities	$ 2,364	$ 21