Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Securities Available For Sale:
Securities available for sale	$ 418,299	$ 409,709
Trading Securities:
Trading securities	7,256	7,150
Certificates of Deposit [Member]
Trading Securities:
Trading securities	170	220
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Securities Available For Sale:
Securities available for sale	943	962
Interest rate swaps	0	0
Trading Securities:
Trading securities	7,204	7,098
Liabilities
Interest rate swaps	0	0
Significant Other Observable Inputs (Level 2) [Member]
Securities Available For Sale:
Securities available for sale	417,356	408,747
Interest rate swaps	146	149
Trading Securities:
Trading securities	52	52
Liabilities
Interest rate swaps	(229)	(310)
Significant Unobservable Inputs (Level 3) [Member]
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 [Member]
Securities Available For Sale:
Securities available for sale	418,299	409,709
Interest rate swaps	146	149
Trading Securities:
Trading securities	7,256	7,150
Liabilities
Interest rate swaps	(229)	(310)
Fair Value Measurement on Recurring Basis [Member] | U.S. Government Sponsored Entities [Member]
Securities Available For Sale:
Securities available for sale	111,921	108,148
Trading Securities:
Trading securities	52	52
Fair Value Measurement on Recurring Basis [Member] | States and Political Subdivisions [Member]
Securities Available For Sale:
Securities available for sale	133,466	137,723
Fair Value Measurement on Recurring Basis [Member] | Residential and Multi-Family Mortgage [Member]
Securities Available For Sale:
Securities available for sale	120,630	109,636
Fair Value Measurement on Recurring Basis [Member] | Corporate Notes and Bonds [Member]
Securities Available For Sale:
Securities available for sale	17,194	17,200
Trading Securities:
Trading securities	250	254
Fair Value Measurement on Recurring Basis [Member] | Pooled SBA [Member]
Securities Available For Sale:
Securities available for sale	34,145	36,040
Fair Value Measurement on Recurring Basis [Member] | Other [Member]
Securities Available For Sale:
Securities available for sale	943	962
Fair Value Measurement on Recurring Basis [Member] | Corporate Equity Securities [Member]
Trading Securities:
Trading securities	5,172	5,125
Fair Value Measurement on Recurring Basis [Member] | Mutual Funds [Member]
Trading Securities:
Trading securities	1,612	1,499
Fair Value Measurement on Recurring Basis [Member] | Certificates of Deposit [Member]
Trading Securities:
Trading securities	170	220
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Securities Available For Sale:
Securities available for sale	943	962
Interest rate swaps	0	0
Trading Securities:
Trading securities	7,204	7,098
Liabilities
Interest rate swaps	0	0
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Government Sponsored Entities [Member]
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | States and Political Subdivisions [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Residential and Multi-Family Mortgage [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Notes and Bonds [Member]
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	250	254
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pooled SBA [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]
Securities Available For Sale:
Securities available for sale	943	962
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Equity Securities [Member]
Trading Securities:
Trading securities	5,172	5,125
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mutual Funds [Member]
Trading Securities:
Trading securities	1,612	1,499
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Certificates of Deposit [Member]
Trading Securities:
Trading securities	170	220
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Securities Available For Sale:
Securities available for sale	417,356	408,747
Interest rate swaps	146	149
Trading Securities:
Trading securities	52	52
Liabilities
Interest rate swaps	(229)	(310)
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Government Sponsored Entities [Member]
Securities Available For Sale:
Securities available for sale	111,921	108,148
Trading Securities:
Trading securities	52	52
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | States and Political Subdivisions [Member]
Securities Available For Sale:
Securities available for sale	133,466	137,723
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Residential and Multi-Family Mortgage [Member]
Securities Available For Sale:
Securities available for sale	120,630	109,636
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Notes and Bonds [Member]
Securities Available For Sale:
Securities available for sale	17,194	17,200
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pooled SBA [Member]
Securities Available For Sale:
Securities available for sale	34,145	36,040
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Equity Securities [Member]
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mutual Funds [Member]
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member]
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
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 [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Government Sponsored Entities [Member]
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | States and Political Subdivisions [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Residential and Multi-Family Mortgage [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate Notes and Bonds [Member]
Securities Available For Sale:
Securities available for sale	0	0
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pooled SBA [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Securities Available For Sale:
Securities available for sale	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate Equity Securities [Member]
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mutual Funds [Member]
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Certificates of Deposit [Member]
Trading Securities:
Trading securities	$ 0	$ 0