Disclosures about Fair Value of Assets and Liabilities - Fair Value Measurements of Assets and Liabilities Recognized on a Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	$ 509,844	$ 439,831
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	17,885	7,989
State and Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	143,483	116,592
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	134,202	137,195
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	212,051	176,726
Private Labeled Mortgage-backed Pools [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	1,830
Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	393	1,329
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	509,844	439,831
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	17,885	7,989
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	143,483	116,592
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	134,202	137,195
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	212,051	176,726
Recurring Basis [Member] | Private Labeled Mortgage-backed Pools [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	1,830
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	393	1,329
Recurring Basis [Member] | Hedged Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	152,216	122,345
Recurring Basis [Member] | Forward Sale Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	286	602
Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	(2,819)	(3,138)
Recurring Basis [Member] | Commitments To Originate Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	(31)	(22)
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	509,844	439,831
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	17,885	7,989
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	143,483	116,592
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	134,202	137,195
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	212,051	176,726
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Private Labeled Mortgage-backed Pools [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	1,830
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	393	1,329
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	152,216	122,345
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	286	602
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	(2,819)	(3,138)
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commitments To Originate Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	$ (31)	$ (22)