Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities Available for Sale Non-Printing (Detail)	Mar. 31, 2015 Security	Dec. 31, 2014 Security
Schedule of Available-for-sale Securities [Line Items]
Number of pooled trust preferred securities	83	96
Pooled Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of pooled trust preferred securities	2	2

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Name:	us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant