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Investment Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Securities	Dec. 31, 2015 USD ($) Securities	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of securities in an unrealized loss position | Securities	82	107
Percentage of combined depreciation of the combined reported value of the aggregate securities portfolio	1.51%	2.44%
OTTI charges incurred	$ 4,646,000		$ 737,000
Carrying amount of available-for-sale securities pledged	$ 139,750,000	$ 236,730,000
Continuous Loss Position More Than Twelve Months
Schedule of Available-for-sale Securities [Line Items]
Number of securities in an unrealized loss position | Securities	15
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
OTTI charges incurred	$ 4,640,000
Non Agency Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
OTTI charges incurred			705,000
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
OTTI charges incurred	$ 11,000	$ 0	$ 32,000

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Number of securities in an unrealized loss position.

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- Definition

Percentage of combined depreciation of the combined reported value of the aggregate securities portfolio.

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- Definition

The fair value of available-for-sale securities that serve as collateral for borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5086-111524

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-URI http://asc.fasb.org/extlink&oid=73527792&loc=SL6284393-111563

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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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