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Investment Securities - Summary of Amortized Cost and Approximate Fair Value of Investment Securities (Detail) - USD ($)
Jun. 30, 2023
Dec. 31, 2022
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost $ 1,258,560,000 $ 840,259,000
Allowance for Credit Losses 0 0
Net Carrying Value 1,258,560,000 840,259,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (46,312,000) (46,446,000)
Fair Value 1,212,248,000 793,813,000
Debt securities, held to maturity, accrued interest 1,400,000 1,000,000
Asset-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 719,551,000 361,107,000
Allowance for Credit Losses 0 0
Net Carrying Value 719,551,000 361,107,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (5,117,000) (4,974,000)
Fair Value 714,434,000 356,133,000
Agency-guaranteed residential mortgage-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 7,115,000 7,189,000
Allowance for Credit Losses 0 0
Net Carrying Value 7,115,000 7,189,000
Gross Unrealized Gains 0
Gross Unrealized Losses (669,000) (563,000)
Fair Value 6,446,000 6,626,000
Agency-guaranteed commercial mortgage-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 1,889,000 1,928,000
Allowance for Credit Losses 0 0
Net Carrying Value 1,889,000 1,928,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (103,000) (104,000)
Fair Value 1,786,000 1,824,000
Agency-guaranteed residential collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 196,206,000 204,495,000
Allowance for Credit Losses 0 0
Net Carrying Value 196,206,000 204,495,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (16,504,000) (18,376,000)
Fair Value 179,702,000 186,119,000
Agency-guaranteed commercial collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 148,066,000 151,711,000
Allowance for Credit Losses 0 0
Net Carrying Value 148,066,000 151,711,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (9,239,000) (9,435,000)
Fair Value 138,827,000 142,276,000
Private label collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 185,733,000 113,829,000
Allowance for Credit Losses 0 0
Net Carrying Value 185,733,000 113,829,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (14,680,000) (12,994,000)
Fair Value $ 171,053,000 $ 100,835,000