Fair Value Measurement - Schedule of Fair Value of Assets and Liabilities Measured on Recurring and Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	$ 13,494	$ 13,457
Total debt securities - available-for-sale	1,796,571	1,261,865
Loans held for sale	12,053	20,320
Other real estate owned and repossessed assets	4,384	5,297
Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	13,494	13,457
Total debt securities - available-for-sale	1,796,571	1,261,865
Loans held for sale	12,053	20,320
Other assets - interest rate derivatives agreements	11,048	7,351
Total assets recurring fair value measurements	1,833,166	1,302,993
Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities - interest rate derivatives agreements	10,832	7,345
Total liabilities recurring fair value measurements	10,832	7,345
Impaired loans		1,717
Other real estate owned and repossessed assets	4,384	5,297
Total assets recurring fair value measurements	4,384	7,014
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	9,913
US Treasury Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	9,913
U.S. Government Sponsored Entities and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	100,682	71,843
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]
Total debt securities - available-for-sale	100,682	71,843
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]
Total debt securities - available-for-sale	1,373,417	934,922
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]
Total debt securities - available-for-sale	1,373,417	934,922
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]
Total debt securities - available-for-sale	140,647	114,867
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]
Total debt securities - available-for-sale	140,647	114,867
Obligations of State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	126,799	104,830
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]
Total debt securities - available-for-sale	126,799	104,830
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	45,113	35,403
Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	45,113	35,403
Investments Measured at Net Asset Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		2,066
Investments Measured at Net Asset Value [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	2,066
Total debt securities - available-for-sale	0	0
Loans held for sale	0	0
Other assets - interest rate derivatives agreements	0	0
Total assets recurring fair value measurements	0	2,066
Investments Measured at Net Asset Value [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities - interest rate derivatives agreements	0	0
Total liabilities recurring fair value measurements	0	0
Impaired loans	0	0
Other real estate owned and repossessed assets	0	0
Total assets recurring fair value measurements	0	0
Investments Measured at Net Asset Value [Member] | US Treasury Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	0
Investments Measured at Net Asset Value [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]
Total debt securities - available-for-sale	0	0
Investments Measured at Net Asset Value [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]
Total debt securities - available-for-sale	0	0
Investments Measured at Net Asset Value [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]
Total debt securities - available-for-sale	0	0
Investments Measured at Net Asset Value [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]
Total debt securities - available-for-sale	0	0
Investments Measured at Net Asset Value [Member] | Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	0	0
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	13,494	11,391
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	13,494	11,391
Total debt securities - available-for-sale	0	0
Loans held for sale	0	0
Other assets - interest rate derivatives agreements	0	0
Total assets recurring fair value measurements	13,494	11,391
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities - interest rate derivatives agreements	0	0
Total liabilities recurring fair value measurements	0	0
Impaired loans	0	0
Other real estate owned and repossessed assets	0	0
Total assets recurring fair value measurements	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | US Treasury Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [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]
Total debt securities - available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [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]
Total debt securities - available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [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]
Total debt securities - available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [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]
Total debt securities - available-for-sale	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities - interest rate derivatives agreements	10,832	7,345
Total debt securities - available-for-sale	1,796,571	1,261,865
Loans held for sale	12,053	20,320
Other assets - interest rate derivatives agreements	11,048	7,351
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]
Equity securities	0	0
Total debt securities - available-for-sale	1,796,571	1,261,865
Loans held for sale	12,053	20,320
Other assets - interest rate derivatives agreements	11,048	7,351
Total assets recurring fair value measurements	1,819,672	1,289,536
Significant Other Observable Inputs (Level 2) [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities - interest rate derivatives agreements	10,832	7,345
Total liabilities recurring fair value measurements	10,832	7,345
Impaired loans	0	0
Other real estate owned and repossessed assets	0	0
Total assets recurring fair value measurements	0	0
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]
Total debt securities - available-for-sale	9,913
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]
Total debt securities - available-for-sale	100,682	71,843
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]
Total debt securities - available-for-sale	1,373,417	934,922
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]
Total debt securities - available-for-sale	140,647	114,867
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]
Total debt securities - available-for-sale	126,799	104,830
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]
Total debt securities - available-for-sale	45,113	35,403
Significant Unobservable Inputs (Level 3) [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Total debt securities - available-for-sale	0	0
Loans held for sale	0	0
Other assets - interest rate derivatives agreements	0	0
Total assets recurring fair value measurements	0	0
Significant Unobservable Inputs (Level 3) [Member] | Nonrecurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities - interest rate derivatives agreements	0	0
Total liabilities recurring fair value measurements	0	0
Impaired loans	0	1,717
Other real estate owned and repossessed assets	4,384	5,297
Total assets recurring fair value measurements	4,384	7,014
Significant Unobservable Inputs (Level 3) [Member] | US Treasury Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	0
Significant Unobservable Inputs (Level 3) [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]
Total debt securities - available-for-sale	0	0
Significant Unobservable Inputs (Level 3) [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]
Total debt securities - available-for-sale	0	0
Significant Unobservable Inputs (Level 3) [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]
Total debt securities - available-for-sale	0	0
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]
Total debt securities - available-for-sale	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Debt Securities [Member] | Recurring Fair Value Measurements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total debt securities - available-for-sale	$ 0	$ 0