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Investment Securities - Summary of Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($)
$ in Thousands
Mar. 31, 2024
Dec. 31, 2023
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 3,333,603 $ 3,398,942
Gross Unrealized Holding Gain, Available-for-sale 61 7,050
Gross Unrealized Holding Loss, Available-for-sale (496,564) (449,867)
Fair Value, Available-for-sale $ 2,837,100 $ 2,956,125
Total Percent, Available-for-sale 100.00% 100.00%
Amortized Cost, Held-to-maturity $ 2,454,586 $ 2,464,610
Gross Unrealized Holding Gain, Held-to-maturity 2,223 3,438
Gross Unrealized Holding Loss, Held-to-maturity (412,778) (385,167)
Fair Value, Held-to-maturity $ 2,044,031 $ 2,082,881
Total Percent, Held-to-maturity 100.00% 100.00%
Government Agency/GSE [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 32,644 $ 32,229
Gross Unrealized Holding Gain, Available-for-sale 0 24
Gross Unrealized Holding Loss, Available-for-sale (4) 0
Fair Value, Available-for-sale $ 32,640 $ 32,253
Total Percent, Available-for-sale 1.15% 1.09%
Amortized Cost, Held-to-maturity $ 526,752 $ 530,656
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (103,672) (97,972)
Fair Value, Held-to-maturity $ 423,080 $ 432,684
Total Percent, Held-to-maturity 21.46% 21.53%
Mortgage-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 2,766,695 $ 2,843,744
Gross Unrealized Holding Gain, Available-for-sale 25 42
Gross Unrealized Holding Loss, Available-for-sale (367,613) (336,107)
Fair Value, Available-for-sale $ 2,399,107 $ 2,507,679
Total Percent, Available-for-sale 84.56% 84.83%
Amortized Cost, Held-to-maturity $ 652,864 $ 663,090
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (109,336) (97,436)
Fair Value, Held-to-maturity $ 543,528 $ 565,654
Total Percent, Held-to-maturity 26.60% 26.90%
CMO/REMIC [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 495,576 $ 502,234
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale (116,682) (112,872)
Fair Value, Available-for-sale $ 378,894 $ 389,362
Total Percent, Available-for-sale 13.35% 13.17%
Amortized Cost, Held-to-maturity $ 798,226 $ 802,892
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (162,528) (156,155)
Fair Value, Held-to-maturity $ 635,698 $ 646,737
Total Percent, Held-to-maturity 32.52% 32.58%
Municipal Bonds [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 26,480 $ 26,477
Gross Unrealized Holding Gain, Available-for-sale 36 46
Gross Unrealized Holding Loss, Available-for-sale (1,372) (888)
Fair Value, Available-for-sale $ 25,144 $ 25,635
Total Percent, Available-for-sale 0.89% 0.87%
Amortized Cost, Held-to-maturity $ 465,289 $ 467,972
Gross Unrealized Holding Gain, Held-to-maturity 2,223 3,438
Gross Unrealized Holding Loss, Held-to-maturity (37,242) (33,604)
Fair Value, Held-to-maturity $ 430,270 $ 437,806
Total Percent, Held-to-maturity 18.96% 18.99%
Other Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 1,315 $ 1,196
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale 0 0
Fair Value, Available-for-sale $ 1,315 $ 1,196
Total Percent, Available-for-sale 0.05% 0.04%
Amortized Cost, Held-to-maturity $ 11,455  
Gross Unrealized Holding Gain, Held-to-maturity 0  
Gross Unrealized Holding Loss, Held-to-maturity 0  
Fair Value, Held-to-maturity $ 11,455  
Total Percent, Held-to-maturity 0.46%  
Unallocated Portfolio Layer Fair Value [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale [1] $ 10,893 $ (6,938)
Gross Unrealized Holding Gain, Available-for-sale [1] 0 6,938
Gross Unrealized Holding Loss, Available-for-sale [1] (10,893) 0
Fair Value, Available-for-sale [1] $ 0 $ 0
Total Percent, Available-for-sale [1] 0.00%  
[1] 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.