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Investment Securities - Summary of Amortized Cost and Approximate Fair Value of Investment Securities (Detail) - USD ($)
Mar. 31, 2024
Dec. 31, 2023
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost $ 1,032,037,000 $ 1,103,170,000
Allowance for Credit Losses 0 0
Net Carrying Value 1,032,037,000 1,103,170,000
Gross Unrealized Gains 345,000 202,000
Gross Unrealized Losses (59,754,000) (56,933,000)
Fair Value 972,628,000 1,046,439,000
Debt securities, held to maturity, accrued interest 2,600,000 2,700,000
Asset-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 509,690,000 575,990,000
Allowance for Credit Losses 0 0
Net Carrying Value 509,690,000 575,990,000
Gross Unrealized Gains 345,000 202,000
Gross Unrealized Losses (2,432,000) (2,064,000)
Fair Value 507,603,000 574,128,000
Agency-guaranteed residential mortgage-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 7,001,000 7,039,000
Allowance for Credit Losses 0 0
Net Carrying Value 7,001,000 7,039,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (1,087,000) (649,000)
Fair Value 5,914,000 6,390,000
Agency-guaranteed commercial mortgage-backed securities    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 1,830,000 1,850,000
Allowance for Credit Losses 0 0
Net Carrying Value 1,830,000 1,850,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (151,000) (134,000)
Fair Value 1,679,000 1,716,000
Agency-guaranteed residential collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 182,856,000 186,636,000
Allowance for Credit Losses 0 0
Net Carrying Value 182,856,000 186,636,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (20,723,000) (19,049,000)
Fair Value 162,133,000 167,587,000
Agency-guaranteed commercial collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 146,001,000 146,765,000
Allowance for Credit Losses 0 0
Net Carrying Value 146,001,000 146,765,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (21,535,000) (23,178,000)
Fair Value 124,466,000 123,587,000
Private label collateralized mortgage obligations    
Schedule of Held-to-Maturity Securities [Line Items]    
Amortized Cost 184,659,000 184,890,000
Allowance for Credit Losses 0 0
Net Carrying Value 184,659,000 184,890,000
Gross Unrealized Gains 0 0
Gross Unrealized Losses (13,826,000) (11,859,000)
Fair Value $ 170,833,000 $ 173,031,000