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, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	$ 507,736	$ 509,665
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	24,284	19,052
State and Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	133,371	149,564
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	133,408	130,365
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	212,173	208,657
Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	390	385
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	4,110	1,642
Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total available-for-sale securities, Fair Value	507,736	509,665
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	24,284	19,052
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	133,371	149,564
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	133,408	130,365
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	212,173	208,657
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	390	385
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	4,110	1,642
Recurring Basis [Member] | Hedged Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	155,013	154,575
Recurring Basis [Member] | Forward Sale Commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	257	143
Recurring Basis [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	2,610	(917)
Recurring Basis [Member] | Commitments To Originate Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, fair value	(4)	(3)
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	507,736	509,665
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	24,284	19,052
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	133,371	149,564
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	133,408	130,365
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	212,173	208,657
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	390	385
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	4,110	1,642
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	155,013	154,575
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	257	143
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	2,610	(917)
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	$ (4)	$ (3)