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Investment Securities - Summary of Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 2,922,404 $ 2,997,047
Gross Unrealized Holding Gain, Available-for-sale 2,226 471
Gross Unrealized Holding Loss, Available-for-sale (389,564) (455,403)
Fair Value, Available-for-sale $ 2,535,066 $ 2,542,115
Total Percent, Available-for-sale 100.00% 100.00%
Amortized Cost, Held-to-maturity $ 2,359,141 $ 2,379,668
Gross Unrealized Holding Gain, Held-to-maturity 482 1,158
Gross Unrealized Holding Loss, Held-to-maturity (394,535) (426,481)
Fair Value, Held-to-maturity $ 1,965,088 $ 1,954,345
Total Percent, Held-to-maturity 100.00% 100.00%
Government Agency/GSE [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 34,757 $ 34,149
Gross Unrealized Holding Gain, Available-for-sale 46 106
Gross Unrealized Holding Loss, Available-for-sale 0 0
Fair Value, Available-for-sale $ 34,803 $ 34,255
Total Percent, Available-for-sale 1.37% 1.35%
Amortized Cost, Held-to-maturity $ 510,593 $ 514,572
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (93,645) (106,315)
Fair Value, Held-to-maturity $ 416,948 $ 408,257
Total Percent, Held-to-maturity 21.64% 21.62%
Mortgage-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 2,398,291 $ 2,460,573
Gross Unrealized Holding Gain, Available-for-sale 1,058 337
Gross Unrealized Holding Loss, Available-for-sale (274,693) (326,376)
Fair Value, Available-for-sale $ 2,124,656 $ 2,134,534
Total Percent, Available-for-sale 83.81% 83.97%
Amortized Cost, Held-to-maturity $ 603,927 $ 614,383
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (99,271) (110,020)
Fair Value, Held-to-maturity $ 504,656 $ 504,363
Total Percent, Held-to-maturity 25.60% 25.82%
CMO/REMIC [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 467,263 $ 471,921
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale (113,401) (120,399)
Fair Value, Available-for-sale $ 353,862 $ 351,522
Total Percent, Available-for-sale 13.96% 13.82%
Amortized Cost, Held-to-maturity $ 777,391 $ 784,059
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (159,636) (170,121)
Fair Value, Held-to-maturity $ 617,755 $ 613,938
Total Percent, Held-to-maturity 32.95% 32.95%
Municipal Bonds [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 21,762 $ 21,755
Gross Unrealized Holding Gain, Available-for-sale 27 28
Gross Unrealized Holding Loss, Available-for-sale (1,470) (1,406)
Fair Value, Available-for-sale $ 20,319 $ 20,377
Total Percent, Available-for-sale 0.80% 0.80%
Amortized Cost, Held-to-maturity $ 454,075 $ 455,199
Gross Unrealized Holding Gain, Held-to-maturity 482 1,158
Gross Unrealized Holding Loss, Held-to-maturity (41,983) (40,025)
Fair Value, Held-to-maturity $ 412,574 $ 416,332
Total Percent, Held-to-maturity 19.25% 19.13%
Other Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 1,426 $ 1,427
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale 0 0
Fair Value, Available-for-sale $ 1,426 $ 1,427
Total Percent, Available-for-sale 0.06% 0.06%
Amortized Cost, Held-to-maturity $ 13,155 [1] $ 11,455 [2]
Gross Unrealized Holding Gain, Held-to-maturity 0 [1] 0 [2]
Gross Unrealized Holding Loss, Held-to-maturity 0 [1] 0 [2]
Fair Value, Held-to-maturity $ 13,155 [1] $ 11,455 [2]
Total Percent, Held-to-maturity 0.56% [1] 0.48% [2]
Unallocated Portfolio Layer Fair Value [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale [3]   $ 7,222
Amortized Cost, Available-for-sale, Unallocated portfolio layer [4] $ (1,095)  
Gross Unrealized Holding Gain, Available-for-sale 1,095 [4] 0 [3]
Gross Unrealized Holding Loss, Available-for-sale 0 [4] (7,222) [3]
Fair Value, Available-for-sale $ 0 [4] $ 0 [3]
Total Percent, Available-for-sale 0.00% [4] 0.00% [3]
[1] Represents Commercial Property Assessed Clean Energy ("C-PACE") bonds.
[2] Represents Commercial Property Assessed Clean Energy ("C-PACE") bonds.
[3] Represents the amount of portfolio layer method basis adjustments related to AFS MBS securities hedged in a closed portfolio. Under U.S. GAAP, portfolio layer method basis adjustments are not allocated to individual securities, however the amounts impact the unrealized gains or losses for the individual securities being hedged. Refer to Note 3 and Note 9 for additional information.
[4] Represents the amount of portfolio layer method basis adjustments related to AFS MBS securities hedged in a closed portfolio. Under U.S. GAAP, portfolio layer method basis adjustments are not allocated to individual securities, however the amounts impact the unrealized gains or losses for the individual securities being hedged. Refer to Note 3 and Note 9 for additional information.