Fair Values of Assets and Liabilities - Schedule of Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	$ (831,223)	$ (902,292)
Assets, Fair Value Disclosure	938,309	962,731
Balance, beginning of period	7,465	4,366
Total gains or losses included in earnings	0	198
Total gains or losses included in other comprehensive income	0	0
Purchases	824	2,956
Issuances	0	0
Sales	0	0
Settlements	0	(55)
Transfers from Level 3	0	0
Transfers into Level 3	0	0
Balance, end of period	8,289	7,465
Other Investments	12,227	16,761
Loans Held-for-sale, Fair Value Disclosure	33,436	15,989
Other Assets, Fair Value Disclosure	60,981	27,689
Other Liabilities, Fair Value Disclosure	61,308	21,469
Financial and Nonfinancial Liabilities, Fair Value Disclosure	61,308	21,469
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	1,670	1,670
Total gains or losses included in earnings	0	0
Total gains or losses included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Transfers from Level 3	0	0
Transfers into Level 3	0	0
Balance, end of period	1,670	1,670
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	5,795	2,696
Total gains or losses included in earnings	0	198
Total gains or losses included in other comprehensive income	0	0
Purchases	824	2,956
Issuances	0	0
Sales	0	0
Settlements	0	(55)
Transfers from Level 3	0	0
Transfers into Level 3	0
Balance, end of period	6,619	5,795
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(24,385)	(23,962)
US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(7,230)	(8,341)
US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(191,180)	(189,133)
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(496,033)	(661,947)
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(100,998)	(1,000)
Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(11,397)	(17,909)
Level 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Assets, Fair Value Disclosure	0	0
Other Investments	0
Loans Held-for-sale, Fair Value Disclosure	0	0
Other Assets, Fair Value Disclosure	0	0
Other Liabilities, Fair Value Disclosure	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Level 1 [Member] | Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Level 1 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Level 1 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(831,223)	(902,292)
Assets, Fair Value Disclosure	930,020	955,266
Other Investments	10,557	15,091
Loans Held-for-sale, Fair Value Disclosure	33,436	15,989
Other Assets, Fair Value Disclosure	54,362	21,894
Other Liabilities, Fair Value Disclosure	61,308	21,469
Financial and Nonfinancial Liabilities, Fair Value Disclosure	61,308	21,469
Fair Value, Inputs, Level 2 [Member] | Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(24,385)	(23,962)
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(7,230)	(8,341)
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(191,180)	(189,133)
Fair Value, Inputs, Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(496,033)	(661,947)
Fair Value, Inputs, Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(100,998)	(1,000)
Fair Value, Inputs, Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(11,397)	(17,909)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Assets, Fair Value Disclosure	8,289	7,465
Loans Held-for-sale, Fair Value Disclosure	0	0
Other Assets, Fair Value Disclosure	6,619	5,795
Other Liabilities, Fair Value Disclosure	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Other Investments	1,670	1,670
Fair Value, Inputs, Level 3 [Member] | Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 3 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	$ 0	$ 0