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Investment Securities - Summary of Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($)
$ in Thousands
Sep. 30, 2023
Dec. 31, 2022
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 3,526,455 $ 3,755,297
Gross Unrealized Holding Gain, Available-for-sale 24 106
Gross Unrealized Holding Loss, Available-for-sale (653,316) (500,192)
Investment securities available-for-sale $ 2,873,163 $ 3,255,211
Total Percent, Available-for-sale 100.00% 100.00%
Amortized Cost, Held-to-maturity $ 2,489,441 $ 2,554,301
Gross Unrealized Holding Gain, Held-to-maturity 4 913
Gross Unrealized Holding Loss, Held-to-maturity (520,127) (399,627)
Fair Value, Held-to-maturity $ 1,969,318 $ 2,155,587
Total Percent, Held-to-maturity 100.00% 100.00%
Government Agency/GSE [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 34,126  
Gross Unrealized Holding Gain, Available-for-sale 0  
Gross Unrealized Holding Loss, Available-for-sale (17)  
Investment securities available-for-sale $ 34,109  
Total Percent, Available-for-sale 1.19%  
Amortized Cost, Held-to-maturity $ 534,814 $ 548,771
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (123,981) (114,343)
Fair Value, Held-to-maturity $ 410,833 $ 434,428
Total Percent, Held-to-maturity 21.48% 21.48%
Mortgage-backed Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 2,925,382 $ 3,192,151
Gross Unrealized Holding Gain, Available-for-sale 1 39
Gross Unrealized Holding Loss, Available-for-sale (488,759) (403,049)
Investment securities available-for-sale $ 2,436,624 $ 2,789,141
Total Percent, Available-for-sale 84.81% 85.68%
Amortized Cost, Held-to-maturity $ 673,413 $ 706,796
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (134,290) (105,867)
Fair Value, Held-to-maturity $ 539,123 $ 600,929
Total Percent, Held-to-maturity 27.05% 27.67%
Municipal Bonds [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 26,799 $ 26,797
Gross Unrealized Holding Gain, Available-for-sale 23 67
Gross Unrealized Holding Loss, Available-for-sale (3,009) (1,177)
Investment securities available-for-sale $ 23,813 $ 25,687
Total Percent, Available-for-sale 0.83% 0.79%
Amortized Cost, Held-to-maturity $ 469,208 $ 471,388
Gross Unrealized Holding Gain, Held-to-maturity 4 913
Gross Unrealized Holding Loss, Held-to-maturity (67,619) (47,687)
Fair Value, Held-to-maturity $ 401,593 $ 424,614
Total Percent, Held-to-maturity 18.85% 18.46%
Other Securities [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 1,119 $ 1,080
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale 0 0
Investment securities available-for-sale $ 1,119 $ 1,080
Total Percent, Available-for-sale 0.04% 0.03%
Unallocated Portfolio Layer Fair Value [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale [1] $ 24,868  
Gross Unrealized Holding Gain, Available-for-sale [1] 0  
Gross Unrealized Holding Loss, Available-for-sale [1] (24,868)  
Investment securities available-for-sale [1] $ 0  
Total Percent, Available-for-sale [1] 0.00%  
CMO/REMIC [Member]    
Schedule of Investments [Line Items]    
Amortized Cost, Available-for-sale $ 514,161 $ 535,269
Gross Unrealized Holding Gain, Available-for-sale 0 0
Gross Unrealized Holding Loss, Available-for-sale (136,663) (95,966)
Investment securities available-for-sale $ 377,498 $ 439,303
Total Percent, Available-for-sale 13.13% 13.50%
Amortized Cost, Held-to-maturity $ 812,006 $ 827,346
Gross Unrealized Holding Gain, Held-to-maturity 0 0
Gross Unrealized Holding Loss, Held-to-maturity (194,237) (131,730)
Fair Value, Held-to-maturity $ 617,769 $ 695,616
Total Percent, Held-to-maturity 32.62% 32.39%
[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 10 for additional information.