Disclosures about Fair Value of Assets and Liabilities - Fair Value Measurements of Assets and Liabilities Recognized on a Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	$ 687,142	$ 600,348
U.S. Treasury and Federal Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	13,995	16,608
State and Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	249,760	209,303
Federal Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	213,043	185,003
Federal Agency Mortgage-backed Pools [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	192,265	178,736
Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	18,079	10,698
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	687,142	600,348
Recurring Basis [Member] | U.S. Treasury and Federal Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	13,995	16,608
Recurring Basis [Member] | State and Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	249,760	209,303
Recurring Basis [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	213,043	185,003
Recurring Basis [Member] | Federal Agency Mortgage-backed Pools [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	192,265	178,736
Recurring Basis [Member] | Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	18,079	10,698
Recurring Basis [Member] | Hedged Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	234,325	209,161
Recurring Basis [Member] | Forward Sale Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	392	135
Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	(6,958)	(1,801)
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	687,142	600,348
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and Federal Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	13,995	16,608
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | State and Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	249,760	209,303
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Federal Agency Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	213,043	185,003
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Federal Agency Mortgage-backed Pools [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	192,265	178,736
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	18,079	10,698
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Hedged Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	234,325	209,161
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Forward Sale Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	392	135
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	$ (6,958)	$ (1,801)