Investment Securities - Summary of Amortized Cost and Estimated Fair Values of Available for Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Amortized Cost	$ 5,153,285	$ 4,031,494
Gross Unrealized Gains	1,325	45,622
Gross Unrealized Losses	341,906	34,417
Allowance For Credit Losses	0	0
Estimated Fair Value	4,812,704	4,042,699
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	502,730	82,136
Gross Unrealized Gains	534	51
Gross Unrealized Losses	10,008	337
Allowance For Credit Losses	0	0
Estimated Fair Value	493,256	81,850
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Amortized Cost	836,622	831,499
Gross Unrealized Gains	240	19,608
Gross Unrealized Losses	85,785	3,809
Allowance For Credit Losses	0	0
Estimated Fair Value	751,077	847,298
Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	1,424,937	1,120,423
Gross Unrealized Gains	178	9,173
Gross Unrealized Losses	130,114	15,822
Allowance For Credit Losses	0	0
Estimated Fair Value	1,295,001	1,113,774
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Amortized Cost	114,692	74,965
Gross Unrealized Gains	198	306
Gross Unrealized Losses	6,252	726
Allowance For Credit Losses	0	0
Estimated Fair Value	108,638	74,545
Commercial Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	686,470	633,802
Gross Unrealized Gains	17	12,731
Gross Unrealized Losses	44,897	6,608
Allowance For Credit Losses	0	0
Estimated Fair Value	641,590	639,925
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	953,347	659,830
Gross Unrealized Gains	15	49
Gross Unrealized Losses	35,738	3,307
Allowance For Credit Losses	0	0
Estimated Fair Value	917,624	656,572
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	17,316	17,291
Gross Unrealized Gains	2	146
Gross Unrealized Losses	1,115	626
Allowance For Credit Losses	0	0
Estimated Fair Value	16,203	16,811
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Amortized Cost	617,171	611,548
Gross Unrealized Gains	141	3,558
Gross Unrealized Losses	27,997	3,182
Allowance For Credit Losses	0	0
Estimated Fair Value	$ 589,315	$ 611,924

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity), and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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