Junior Subordinated Debentures Held by Trusts that Issued Capital Debt - Additional Information (Detail) - USD ($)		12 Months Ended
Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2009
Debt Instrument [Line Items]
Junior subordinated debentures issued	$ 92,800,000	$ 92,800,000	$ 92,800,000
Common capital securities	$ 2,800,000	$ 2,800,000	$ 2,800,000
Tier 1 capital limitation, interest	25.00%	25.00%
Limited capital securities and other restricted core capital elements, net of goodwill	25.00%	25.00%
Capital securities qualified as Tier 1 capital	$ 62,000,000	$ 62,000,000
Tier 2 capital elements	25.00%	25.00%
Junior subordinated debentures interest rate description		The three-month LIBOR rate at December 31, 2016 was 1.00%.
Junior subordinated debentures interest rate	1.00%
Cash balance available to pay junior subordinated debenture interest obligations	$ 27,000,000	$ 27,000,000
Maximum [Member]
Debt Instrument [Line Items]
Capital securities qualified as Tier 1 capital				$ 15,000,000,000

Junior subordinated debentures issued.

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- Definition

Limited capital securities and other restricted core capital elements interest.

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Tier 2 risk based capital to risk weighted assets.

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Amount of cash eligible for distribution to members or limited partners of limited liability company (LLC) or limited partnership (LP), subject to reserves to be maintained as defined in operating or partnership agreement, or in a credit facility agreement.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The amount of excess Tier 1 Risk Based Capital (which consists of the types of financial capital considered the most reliable and liquid, primarily Shareholders' equity. Examples of Tier 1 capital are common stock or unit, preferred stock or unit that is irredeemable and noncumulative, and retained earnings) divided by risk-weighted assets which are assets that are weighted for credit risk according to a formula used by the Reserve Bank.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
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- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Tier 1 Risk Based Capital as defined in the regulations.

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