Investment Securities - Gross Gains and (Losses) on Sales of Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Gross gains	$ 1,048us-gaap_GainOnSaleOfInvestments	$ 366us-gaap_GainOnSaleOfInvestments
Gross (losses)	(459)us-gaap_LossOnSaleOfInvestments	0us-gaap_LossOnSaleOfInvestments
Net (losses) gains	$ 589us-gaap_GainLossOnSaleOfInvestments	$ 366us-gaap_GainLossOnSaleOfInvestments

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.

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

Name:	us-gaap_GainLossOnSaleOfInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration