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Fair Values of Assets and Liabilities - Quantitative Inputs and Assumptions Used in Level 3 Fair Value Measurements (Detail) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 829,181,000 | $ 966,548,000
Other Assets, Fair Value Disclosure | 7,019,000 | 11,273,000
Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | 35,892,000 | 37,828,000
Other Assets, Fair Value Disclosure | 930,000 | 0
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 33,292,000 |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Probability Of Default [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Probability of default |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Prepayment Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Prepayment rates |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Discount Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Discount rates |
Other Assets [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Valuation Techniques | Discounted Cash Flow |
Other Assets [Member] | Par Value [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Valuation Techniques | Par Value |
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 1,670,000 |
Equity Securities [Member] | Par Value [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Valuation Techniques | Par Value |
Impaired Loans [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 9,303,000 |
Fair Value Measurements, Valuation Techniques | Discounted Cash Flow |
Impaired Loans [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 2,281,000 |
Fair Value Measurements, Valuation Techniques | Gas Reserve study |
Impaired Loans [Member] | Discount Rates [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Discount Rate |
Impaired Loans [Member] | Discount Rates [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Discount rate |
Impaired Loans [Member] | Gas Per Million Cubic Feet [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Gas per MCF |
Impaired Loans [Member] | Oil Per Barrels Per Day [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Measurements, Significant Assumptions | Oil per BBL/d |
Fair Value, Measurements, Nonrecurring [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 46,235,000 | 53,846,000
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Assets, Fair Value Disclosure | $ 19,990,000 | $ 12,828,000
Maximum [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 4.68% |
Maximum [Member] | Probability Of Default [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 10000.00% |
Maximum [Member] | Prepayment Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 7266.00% |
Maximum [Member] | Gas Per Million Cubic Feet [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Weighted Average Inputs Price | $ 3.38 |
Maximum [Member] | Oil Per Barrels Per Day [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Weighted Average Inputs Price | $ 56.16 |
Maximum [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member] | Discount Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 1200.00% |
Weighted Average [Member] | Probability Of Default [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 1067.00% |
Weighted Average [Member] | Prepayment Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 415.00% |
Weighted Average [Member] | Impaired Loans [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 10.00% |
Minimum [Member] | Discounted Cash Flow [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 1.90% |
Minimum [Member] | Probability Of Default [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 0.00% |
Minimum [Member] | Prepayment Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 0.00% |
Minimum [Member] | Gas Per Million Cubic Feet [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Weighted Average Inputs Price | $ 1.63 |
Minimum [Member] | Oil Per Barrels Per Day [Member] | Reserve [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Weighted Average Inputs Price | $ 40.97 |
Minimum [Member] | Pooled Trust Preferred Collateralized Debt Obligations [Member] | Discount Rates [Member] |  |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |  |
Fair Value Inputs, Discount Rate | 525.00% |

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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 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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