Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Securities Available For Sale:
Securities available for sale	$ 409,709	$ 495,835
Trading Securities:
Trading securities	7,150	4,858
Certificates of Deposit [Member]
Trading Securities:
Trading securities	220	202
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Securities Available For Sale:
Securities available for sale	962	971
Interest rate swaps	0	0
Trading Securities:
Trading securities	7,098	4,805
Liabilities
Interest rate swaps	0	0
Significant Other Observable Inputs (Level 2) [Member]
Securities Available For Sale:
Securities available for sale	408,747	492,815
Interest rate swaps	149	211
Trading Securities:
Trading securities	52	53
Liabilities
Interest rate swaps	(310)	(670)
Significant Unobservable Inputs (Level 3) [Member]
Securities Available For Sale:
Securities available for sale	0	2,049
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	409,709	495,835
Interest rate swaps	149	211
Trading Securities:
Trading securities	7,150	4,858
Liabilities
Interest rate swaps	(310)	(670)
Fair Value Measurement on Recurring Basis [Member] | U.S. Government Sponsored Entities [Member]
Securities Available For Sale:
Securities available for sale	108,148	140,351
Trading Securities:
Trading securities	52	53
Fair Value Measurement on Recurring Basis [Member] | States and Political Subdivisions [Member]
Securities Available For Sale:
Securities available for sale	137,723	157,037
Fair Value Measurement on Recurring Basis [Member] | Residential and Multi-Family Mortgage [Member]
Securities Available For Sale:
Securities available for sale	109,636	134,976
Fair Value Measurement on Recurring Basis [Member] | Corporate Notes and Bonds [Member]
Securities Available For Sale:
Securities available for sale	17,200	17,414
Trading Securities:
Trading securities	254	254
Fair Value Measurement on Recurring Basis [Member] | Pooled Trust Preferred [Member]
Securities Available For Sale:
Securities available for sale		2,049
Fair Value Measurement on Recurring Basis [Member] | Pooled SBA [Member]
Securities Available For Sale:
Securities available for sale	36,040	43,037
Fair Value Measurement on Recurring Basis [Member] | Other Equity Securities [Member]
Securities Available For Sale:
Securities available for sale	962	971
Fair Value Measurement on Recurring Basis [Member] | Corporate Equity Securities [Member]
Trading Securities:
Trading securities	5,125	3,312
Fair Value Measurement on Recurring Basis [Member] | Mutual Funds [Member]
Trading Securities:
Trading securities	1,499	1,037
Fair Value Measurement on Recurring Basis [Member] | Certificates of Deposit [Member]
Trading Securities:
Trading securities	220	202
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	962	971
Interest rate swaps	0	0
Trading Securities:
Trading securities	7,098	4,805
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	254	254
Fair Value Measurement on Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pooled Trust Preferred [Member]
Securities Available For Sale:
Securities available for sale		0
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 Equity Securities [Member]
Securities Available For Sale:
Securities available for sale	962	971
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	5,125	3,312
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	1,499	1,037
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	220	202
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Securities Available For Sale:
Securities available for sale	408,747	492,815
Interest rate swaps	149	211
Trading Securities:
Trading securities	52	53
Liabilities
Interest rate swaps	(310)	(670)
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	108,148	140,351
Trading Securities:
Trading securities	52	53
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	137,723	157,037
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	109,636	134,976
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	17,200	17,414
Trading Securities:
Trading securities	0	0
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pooled Trust Preferred [Member]
Securities Available For Sale:
Securities available for sale		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	36,040	43,037
Fair Value Measurement on Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other Equity Securities [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	2,049
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 Trust Preferred [Member]
Securities Available For Sale:
Securities available for sale		2,049
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 Equity Securities [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