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, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	$ (902,292)	$ (909,247)
Assets, Fair Value Disclosure	962,731	957,719
Balance, beginning of period	4,366	27,459
Total gains or losses included in earnings	198	8,102
Total gains or losses included in other comprehensive income	0	(118)
Purchases	2,956	601
Issuances	0	0
Sales	0	(12,289)
Settlements	(55)	(19,389)
Transfers from Level 3	0	0
Transfers into Level 3	0	0
Balance, end of period	7,465	4,366
Other Investments	16,761	32,126
Loans Held-for-sale, Fair Value Disclosure	15,989	11,881
Other Assets, Fair Value Disclosure	27,689	4,465
Other Liabilities, Fair Value Disclosure	21,469	2,081
Financial and Nonfinancial Liabilities, Fair Value Disclosure	21,469	2,081
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	0	23,646
Total gains or losses included in earnings		8,102
Total gains or losses included in other comprehensive income		(118)
Purchases		0
Issuances		0
Sales		(12,289)
Settlements		(19,341)
Transfers from Level 3		0
Transfers into Level 3		0
Balance, end of period		0
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	2,696	2,143
Total gains or losses included in earnings	198	0
Total gains or losses included in other comprehensive income	0	0
Purchases	2,956	601
Issuances	0	0
Sales	0	0
Settlements	55	(48)
Transfers from Level 3	0	0
Transfers into Level 3	0
Balance, end of period	5,795	2,696
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Securities available for sale, at fair value	(23,962)	(21,012)
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	(8,341)	(9,406)
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	(189,133)	(167,744)
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	(661,947)	(673,361)
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	(1,000)	(10,012)
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	(17,909)	(27,712)
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	(902,292)	(909,247)
Assets, Fair Value Disclosure	955,266	953,353
Other Investments	15,091	30,456
Loans Held-for-sale, Fair Value Disclosure	15,989	11,881
Other Assets, Fair Value Disclosure	21,894	1,769
Other Liabilities, Fair Value Disclosure	21,469	2,081
Financial and Nonfinancial Liabilities, Fair Value Disclosure	21,469	2,081
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	(23,962)	(21,012)
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	(8,341)	(9,406)
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	(189,133)	(167,744)
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	(661,947)	(673,361)
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	(1,000)	(10,012)
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	(17,909)	(27,712)
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	7,465	4,366
Loans Held-for-sale, Fair Value Disclosure	0	0
Other Assets, Fair Value Disclosure	5,795	2,696
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