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Investment Securities - Summary of Amortized Cost and Approximate Fair Value of Investment Securities (Detail) - USD ($)
Sep. 30, 2023
Dec. 31, 2022
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost $ 1,178,370,000 $ 840,259,000
Allowance for Credit Losses 0 0
Net Carrying Value 1,178,370,000 840,259,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (62,794,000) (46,446,000)
Fair Value 1,115,576,000 793,813,000
Debt securities, held to maturity, accrued interest 2,700,000 1,000,000
Asset-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 645,362,000 361,107,000
Allowance for Credit Losses 0 0
Net Carrying Value 645,362,000 361,107,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (5,174,000) (4,974,000)
Fair Value 640,188,000 356,133,000
Agency-guaranteed residential mortgage-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 7,077,000 7,189,000
Allowance for Credit Losses 0 0
Net Carrying Value 7,077,000 7,189,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (1,027,000) (563,000)
Fair Value 6,050,000 6,626,000
Agency-guaranteed commercial mortgage-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 1,870,000 1,928,000
Allowance for Credit Losses 0 0
Net Carrying Value 1,870,000 1,928,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (139,000) (104,000)
Fair Value 1,731,000 1,824,000
Agency-guaranteed residential collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 191,469,000 204,495,000
Allowance for Credit Losses 0 0
Net Carrying Value 191,469,000 204,495,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (23,331,000) (18,376,000)
Fair Value 168,138,000 186,119,000
Agency-guaranteed commercial collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 147,414,000 151,711,000
Allowance for Credit Losses 0 0
Net Carrying Value 147,414,000 151,711,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (15,848,000) (9,435,000)
Fair Value 131,566,000 142,276,000
Private label collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 185,178,000 113,829,000
Allowance for Credit Losses 0 0
Net Carrying Value 185,178,000 113,829,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (17,275,000) (12,994,000)
Fair Value $ 167,903,000 $ 100,835,000