Fair Value Measurement - Schedule of Fair Value of Assets and Liabilities Measured on Recurring and Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	$ 11,230	$ 12,343
Available-for-sale debt securities	2,262,082	2,393,558
Loans held for sale	48,021	43,013
Other real estate owned and repossessed assets	1,083	4,178
Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	11,230	12,343
Available-for-sale debt securities	2,262,082	2,393,558
Loans held for sale	48,021	43,013
Other assets - interest rate derivatives agreements	48,182	14,585
Total assets	2,369,515	2,463,499
Other liabilities - interest rate derivatives agreements	52,464	16,117
Total liabilities recurring fair value measurements	52,464	16,117
Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually-evaluated nonperforming loans	2,439
Impaired Loans		2,362
Other real estate owned and repossessed assets	1,032	4,178
Total assets	3,471	6,540
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	21,508	32,836
US Treasury Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	21,508	32,836
U.S. Government Sponsored Entities and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	159,379	159,628
U.S. Government Sponsored Entities and Agencies [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	159,379	159,628
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	1,671,469	1,815,987
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	1,671,469	1,815,987
Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	223,827	190,409
Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	223,827	190,409
Obligations of State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	141,573	145,609
Obligations of State and Political Subdivisions [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	141,573	145,609
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	44,326	49,089
Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	44,326	49,089
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	11,230	12,343
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	11,230	12,343
Total assets	11,230	12,343
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	2,260,506	2,391,953
Loans held for sale	48,021	43,013
Other assets - interest rate derivatives agreements	48,182	14,585
Other liabilities - interest rate derivatives agreements	52,464	16,117
Significant Other Observable Inputs (Level 2) [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	2,260,506	2,391,953
Loans held for sale	48,021	43,013
Other assets - interest rate derivatives agreements	48,182	14,585
Total assets	2,356,709	2,449,551
Other liabilities - interest rate derivatives agreements	52,464	16,117
Total liabilities recurring fair value measurements	52,464	16,117
Significant Other Observable Inputs (Level 2) [Member] | US Treasury Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	21,508	32,836
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Sponsored Entities and Agencies [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	159,379	159,628
Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	1,671,469	1,815,987
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Sponsored Entities and Agencies [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	223,827	190,409
Significant Other Observable Inputs (Level 2) [Member] | Obligations of State and Political Subdivisions [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	139,997	144,004
Significant Other Observable Inputs (Level 2) [Member] | Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	44,326	49,089
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	1,576	1,605
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	1,576	1,605
Total assets	1,576	1,605
Significant Unobservable Inputs (Level 3) [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Individually-evaluated nonperforming loans	2,439
Impaired Loans		2,362
Other real estate owned and repossessed assets	1,032	4,178
Total assets	3,471	6,540
Significant Unobservable Inputs (Level 3) [Member] | Obligations of State and Political Subdivisions [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale debt securities	$ 1,576	$ 1,605