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Investment Securities - Summary of Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($)
$ in Thousands
Sep. 30, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Amortized cost $ 2,902,365 $ 2,997,047
Gross Unrealized Holding Gain, Available-for-sale 13,866 471
Gross Unrealized Holding Loss, Available-for-sale (336,834) (455,403)
Investment securities available-for-sale $ 2,579,397 $ 2,542,115
Total Percent, Available-for-sale 100.00% 100.00%
Amortized Cost, Held-to-maturity $ 2,297,909 $ 2,379,668
Gross Unrealized Holding Gain, Held-to-maturity 863 1,158
Gross Unrealized Holding Loss, Held-to-maturity (362,874) (426,481)
Fair Value, Held-to-maturity $ 1,935,898 $ 1,954,345
Total Percent, Held-to-maturity 100.00% 100.00%
Government Agency/GSE [Member]    
Schedule of Investments [Line Items]    
Amortized cost $ 34,738 $ 34,149
Gross Unrealized Holding Gain, Available-for-sale 14 106
Gross Unrealized Holding Loss, Available-for-sale 0 0
Investment securities available-for-sale $ 34,752 $ 34,255
Total Percent, Available-for-sale 1.35% 1.35%
Amortized Cost, Held-to-maturity $ 502,460 $ 514,572
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (86,096) (106,315)
Fair Value, Held-to-maturity $ 416,364 $ 408,257
Total Percent, Held-to-maturity 21.87% 21.62%
Mortgage-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized cost $ 2,186,896 $ 2,460,573
Gross Unrealized Holding Gain, Available-for-sale 1,810 337
Gross Unrealized Holding Loss, Available-for-sale (225,199) (326,376)
Investment securities available-for-sale $ 1,963,507 $ 2,134,534
Total Percent, Available-for-sale 76.13% 83.97%
Amortized Cost, Held-to-maturity $ 570,690 $ 614,383
Gross Unrealized Holding Gain, Held-to-maturity 2 0
Gross Unrealized Holding Loss, Held-to-maturity (87,814) (110,020)
Fair Value, Held-to-maturity $ 482,878 $ 504,363
Total Percent, Held-to-maturity 24.84% 25.82%
Municipal Bonds [Member]    
Schedule of Investments [Line Items]    
Amortized cost $ 21,778 $ 21,755
Gross Unrealized Holding Gain, Available-for-sale 34 28
Gross Unrealized Holding Loss, Available-for-sale (609) (1,406)
Investment securities available-for-sale $ 21,203 $ 20,377
Total Percent, Available-for-sale 0.82% 0.80%
Amortized Cost, Held-to-maturity $ 446,881 $ 455,199
Gross Unrealized Holding Gain, Held-to-maturity 861 1,158
Gross Unrealized Holding Loss, Held-to-maturity (31,602) (40,025)
Fair Value, Held-to-maturity $ 416,140 $ 416,332
Total Percent, Held-to-maturity 19.45% 19.13%
Other Securities [Member]    
Schedule of Investments [Line Items]    
Amortized cost $ 1,656 $ 1,427
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale 0 0
Investment securities available-for-sale $ 1,656 $ 1,427
Total Percent, Available-for-sale 0.06% 0.06%
Amortized Cost, Held-to-maturity $ 17,685 [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 $ 17,685 [1] $ 11,455 [2]
Total Percent, Held-to-maturity 0.77% [1] 0.48% [2]
Unallocated Portfolio Layer Fair Value [Member]    
Schedule of Investments [Line Items]    
Amortized cost $ (10,838) [3] $ 7,222 [4]
Gross Unrealized Holding Gain, Available-for-sale 10,838 [3] 0 [4]
Gross Unrealized Holding Loss, Available-for-sale 0 [3] (7,222) [4]
Investment securities available-for-sale $ 0 [3] $ 0 [4]
Total Percent, Available-for-sale 0.00% [3] 0.00% [4]
CMO/REMIC [Member]    
Schedule of Investments [Line Items]    
Amortized cost $ 668,135 $ 471,921
Gross Unrealized Holding Gain, Available-for-sale 1,170 0
Gross Unrealized Holding Loss, Available-for-sale (111,026) (120,399)
Investment securities available-for-sale $ 558,279 $ 351,522
Total Percent, Available-for-sale 21.64% 13.82%
Amortized Cost, Held-to-maturity $ 760,193 $ 784,059
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (157,362) (170,121)
Fair Value, Held-to-maturity $ 602,831 $ 613,938
Total Percent, Held-to-maturity 33.07% 32.95%
[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.