Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Securities Available For Sale:
Securities available for sale	$ 450,895	$ 409,709
Fair Value Measurement on Recurring Basis
Securities Available For Sale:
Securities available for sale	450,895	409,709
Interest Rate swaps	153	149
Trading Securities:
Trading securities	7,545	7,150
LIABILITIES
Interest rate swaps	(189)	(310)
Fair Value Measurement on Recurring Basis | U.S. Government sponsored entities
Securities Available For Sale:
Securities available for sale	124,432	108,148
Trading Securities:
Trading securities	51	52
Fair Value Measurement on Recurring Basis | States and political subdivisions
Securities Available For Sale:
Securities available for sale	134,267	137,723
Fair Value Measurement on Recurring Basis | Residential and multi-family mortgage
Securities Available For Sale:
Securities available for sale	146,467	109,636
Fair Value Measurement on Recurring Basis | Corporate notes and bonds
Securities Available For Sale:
Securities available for sale	12,855	17,200
Trading Securities:
Trading securities	248	254
Fair Value Measurement on Recurring Basis | Pooled SBA
Securities Available For Sale:
Securities available for sale	31,939	36,040
Fair Value Measurement on Recurring Basis | Other
Securities Available For Sale:
Securities available for sale	935	962
Fair Value Measurement on Recurring Basis | Corporate equity securities
Trading Securities:
Trading securities	5,398	5,125
Fair Value Measurement on Recurring Basis | Mutual funds
Trading Securities:
Trading securities	1,626	1,499
Fair Value Measurement on Recurring Basis | Certificates of deposit
Trading Securities:
Trading securities	222	220
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Securities Available For Sale:
Securities available for sale	935	962
Interest Rate swaps	0	0
Trading Securities:
Trading securities	7,494	7,098
LIABILITIES
Interest rate swaps	0	0
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government sponsored entities
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | States and political subdivisions
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential and multi-family mortgage
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate notes and bonds
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	248	254
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled SBA
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Securities Available For Sale:
Securities available for sale	935	962
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate equity securities
Trading Securities:
Trading securities	5,398	5,125
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Trading Securities:
Trading securities	1,626	1,499
Fair Value Measurement on Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Certificates of deposit
Trading Securities:
Trading securities	222	220
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2)
Securities Available For Sale:
Securities available for sale	449,960	408,747
Interest Rate swaps	153	149
Trading Securities:
Trading securities	51	52
LIABILITIES
Interest rate swaps	(189)	(310)
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | U.S. Government sponsored entities
Securities Available For Sale:
Securities available for sale	124,432	108,148
Trading Securities:
Trading securities	51	52
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | States and political subdivisions
Securities Available For Sale:
Securities available for sale	134,267	137,723
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Residential and multi-family mortgage
Securities Available For Sale:
Securities available for sale	146,467	109,636
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Corporate notes and bonds
Securities Available For Sale:
Securities available for sale	12,855	17,200
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Pooled SBA
Securities Available For Sale:
Securities available for sale	31,939	36,040
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Other
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Corporate equity securities
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Mutual funds
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Other Observable Inputs (Level 2) | Certificates of deposit
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3)
Securities Available For Sale:
Securities available for sale	0	0
Interest Rate swaps	0	0
Trading Securities:
Trading securities	0	0
LIABILITIES
Interest rate swaps	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | U.S. Government sponsored entities
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | States and political subdivisions
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Residential and multi-family mortgage
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Corporate notes and bonds
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Pooled SBA
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Other
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Corporate equity securities
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Mutual funds
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis | Significant Unobservable Inputs (Level 3) | Certificates of deposit
Trading Securities:
Trading securities	$ 0	$ 0