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Investment Securities - Summary of Amortized Cost and Approximate Fair Value of Investment Securities (Detail) - USD ($)
$ in Thousands
Mar. 31, 2022
Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost $ 4,232,729 $ 3,799,851
Allowance for Credit Losses (728)  
Gross Unrealized Gains 2,296 7,427
Gross Unrealized Losses (90,268) (15,703)
Fair Value 4,144,029 3,791,575
Equity securities 25,824 25,575
Investment securities, at fair value 4,169,853 3,817,150
Available-for-sale debt securities, accrued interest 14,300 11,000
Asset-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 351,847 297,291
Allowance for Credit Losses (728)  
Gross Unrealized Gains 87 253
Gross Unrealized Losses (7,587) (119)
Fair Value 343,619 297,425
Agency-guaranteed residential mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 9,242 9,865
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 0
Gross Unrealized Losses (973) (312)
Fair Value 8,269 9,553
Agency-guaranteed commercial mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 2,140 2,162
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 0
Gross Unrealized Losses (95) (10)
Fair Value 2,045 2,152
Agency-guaranteed residential collateralized mortgage obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 618,998 199,091
Allowance for Credit Losses 0  
Gross Unrealized Gains 833 154
Gross Unrealized Losses (16,428) (2,315)
Fair Value 603,403 196,930
Agency-guaranteed commercial collateralized mortgage obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 172,410 242,668
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 53
Gross Unrealized Losses (9,811) (3,877)
Fair Value 162,599 238,844
Collateralized loan obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 1,010,938 1,067,770
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 247
Gross Unrealized Losses (6,576) (1,215)
Fair Value 1,004,362 1,066,802
Commercial mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 148,993 149,054
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 53
Gross Unrealized Losses (1,368) (180)
Fair Value 147,625 148,927
Corporate notes    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 607,230 575,273
Allowance for Credit Losses 0  
Gross Unrealized Gains 1,376 6,334
Gross Unrealized Losses (14,856) (1,561)
Fair Value 593,750 580,046
Private label collateralized mortgage obligations    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 1,302,400 1,248,142
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 333
Gross Unrealized Losses (31,993) (6,010)
Fair Value 1,270,407 1,242,465
State and political subdivision debt securities    
Debt Securities, Available-for-sale [Line Items]    
Amortized Cost 8,531 8,535
Allowance for Credit Losses 0  
Gross Unrealized Gains 0 0
Gross Unrealized Losses (581) (104)
Fair Value $ 7,950 $ 8,431