Investment Securities - Schedule of Realized Gains and Losses from Sale of Securities Classified as Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Realized gains									$ 863	$ 2,387	$ 3,754
Realized losses									(92)	(110)	(15)
Net realized gains (losses)	$ 164us-gaap_GainLossOnSaleOfInvestments	$ 582us-gaap_GainLossOnSaleOfInvestments	$ 8us-gaap_GainLossOnSaleOfInvestments	$ 19us-gaap_GainLossOnSaleOfInvestments	$ 19us-gaap_GainLossOnSaleOfInvestments	$ 13us-gaap_GainLossOnSaleOfInvestments	$ (57)us-gaap_GainLossOnSaleOfInvestments	$ 2,359us-gaap_GainLossOnSaleOfInvestments	$ 771us-gaap_GainLossOnSaleOfInvestments	$ 2,277us-gaap_GainLossOnSaleOfInvestments	$ 3,739us-gaap_GainLossOnSaleOfInvestments

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

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- Definition

This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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- Definition

The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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