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Fair Values of Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	$ 731,358	$ 778,612
Other investments	29,837	36,498
Loans Held for Sale	14,850	7,052
Other Assets	3,921	7,019
Total Assets	779,966	829,181
Other Liabilities	3,079	5,972
Total Liabilities	3,079	5,972
US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	11,338	16,617
US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	24,149
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	625,555	676,853
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	1
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	1,097	16,631
Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	27,410	27,229
Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	16,493	6,319
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	23,646	33,292
Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	729,688	776,942
Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	1,670	1,670
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Other investments	0	0
Loans Held for Sale	0	0
Other Assets	0	0
Total Assets	0	0
Other Liabilities	0	0
Total Liabilities	0	0
Level 1 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 1 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	706,042	743,650
Other investments	29,837	36,498
Loans Held for Sale	14,850	7,052
Other Assets	1,778	6,089
Total Assets	752,507	793,289
Other Liabilities	3,079	5,972
Total Liabilities	3,079	5,972
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	11,338	16,617
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	24,149
Fair Value, Inputs, Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	625,555	676,853
Fair Value, Inputs, Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	1
Fair Value, Inputs, Level 2 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	1,097	16,631
Fair Value, Inputs, Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	27,410	27,229
Fair Value, Inputs, Level 2 [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	16,493	6,319
Fair Value, Inputs, Level 2 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	706,042	743,650
Total Assets	23,646
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	25,316	34,962
Other investments	0	0
Loans Held for Sale	0	0
Other Assets	2,143	930
Total Assets	27,459	35,892
Other Liabilities	0	0
Total Liabilities	0	0
Level 3 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total Assets	1,670
Level 3 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member] | US Government Agencies Debt Securities [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Residential [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage-Backed Securities-Commercial [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member] | Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member] | Corporate Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	0	0
Level 3 [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale	$ 23,646	33,292
Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale		33,292
Level 3 [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value of Available for Sale		$ 1,670

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 320
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Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

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-Publisher FASB
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Fair value of financial and nonfinancial obligations.

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