Fair Value of Assets and Liabilities - Summary Of The Balances Of Assets And Liabilities Measured At Fair Value On A Recurring Basis (Detail) - Fair Value, Recurring - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets
Rabbi trust investments	$ 87,292	$ 104,372
Loans held for sale	1,166	1,206
Customer-related positions	23,725	64,338
Risk participation agreements	196	315
Matched customer book	91	61
Foreign currency loan	7
Mortgage derivatives	239	256
Total	8,030,021	8,681,772
Liabilities
Customer-related positions	24,988	17,880
Risk participation agreements	401	580
Matched customer book	78	46
Foreign currency loan	16	87
Mortgage derivatives	168	16
Total	25,651	18,609
Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale	4,969,346	5,524,708
Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale	1,615,927	1,408,868
U.S. Agency bonds
Assets
Securities available for sale	1,013,899	1,175,014
U.S. Treasury securities
Assets
Securities available for sale	56,235	88,605
State and municipal bonds and obligations
Assets
Securities available for sale	260,316	280,329
Small Business Administration pooled securities
Assets
Securities available for sale		32,103
Other debt securities
Assets
Securities available for sale	1,582	1,597
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Rabbi trust investments	79,189	96,190
Loans held for sale	0	0
Customer-related positions	0	0
Risk participation agreements	0	0
Matched customer book	0	0
Foreign currency loan	0
Mortgage derivatives	0	0
Total	135,424	184,795
Liabilities
Customer-related positions	0	0
Risk participation agreements	0	0
Matched customer book	0	0
Foreign currency loan	0	0
Mortgage derivatives	0	0
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Agency bonds
Assets
Securities available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| U.S. Treasury securities
Assets
Securities available for sale	56,235	88,605
Quoted Prices in Active Markets for Identical Assets (Level 1) \| State and municipal bonds and obligations
Assets
Securities available for sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Small Business Administration pooled securities
Assets
Securities available for sale		0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Other debt securities
Assets
Securities available for sale	0	0
Significant Other Observable Inputs (Level 2)
Assets
Rabbi trust investments	8,103	8,182
Loans held for sale	1,166	1,206
Customer-related positions	23,725	64,338
Risk participation agreements	196	315
Matched customer book	91	61
Foreign currency loan	7
Mortgage derivatives	239	256
Total	7,894,597	8,496,977
Liabilities
Customer-related positions	24,988	17,880
Risk participation agreements	401	580
Matched customer book	78	46
Foreign currency loan	16	87
Mortgage derivatives	168	16
Total	25,651	18,609
Significant Other Observable Inputs (Level 2) \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale	4,969,346	5,524,708
Significant Other Observable Inputs (Level 2) \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale	1,615,927	1,408,868
Significant Other Observable Inputs (Level 2) \| U.S. Agency bonds
Assets
Securities available for sale	1,013,899	1,175,014
Significant Other Observable Inputs (Level 2) \| U.S. Treasury securities
Assets
Securities available for sale	0	0
Significant Other Observable Inputs (Level 2) \| State and municipal bonds and obligations
Assets
Securities available for sale	260,316	280,329
Significant Other Observable Inputs (Level 2) \| Small Business Administration pooled securities
Assets
Securities available for sale		32,103
Significant Other Observable Inputs (Level 2) \| Other debt securities
Assets
Securities available for sale	1,582	1,597
Significant Unobservable Inputs (Level 3)
Assets
Rabbi trust investments	0	0
Loans held for sale	0	0
Customer-related positions	0	0
Risk participation agreements	0	0
Matched customer book	0	0
Foreign currency loan	0
Mortgage derivatives	0	0
Total	0	0
Liabilities
Customer-related positions	0	0
Risk participation agreements	0	0
Matched customer book	0	0
Foreign currency loan	0	0
Mortgage derivatives	0	0
Total	0	0
Significant Unobservable Inputs (Level 3) \| Government-sponsored residential mortgage-backed securities
Assets
Securities available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Government-sponsored commercial mortgage-backed securities
Assets
Securities available for sale	0	0
Significant Unobservable Inputs (Level 3) \| U.S. Agency bonds
Assets
Securities available for sale	0	0
Significant Unobservable Inputs (Level 3) \| U.S. Treasury securities
Assets
Securities available for sale	0	0
Significant Unobservable Inputs (Level 3) \| State and municipal bonds and obligations
Assets
Securities available for sale	0	0
Significant Unobservable Inputs (Level 3) \| Small Business Administration pooled securities
Assets
Securities available for sale		0
Significant Unobservable Inputs (Level 3) \| Other debt securities
Assets
Securities available for sale	$ 0	$ 0

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