Investment Securities - Changes in Credit Loss Component of Cumulative Other-than-Temporary Impairment Losses on Debt Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014	Mar. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Balance, beginning of period			$ 9,990	$ 33,290	$ 9,682	$ 33,102
Reductions: Accretion of credit loss impairment due to an increase in expected cash flows	(198)	(190)	(506)	(378)
Balance, end of period	$ 9,484	$ 32,912	$ 9,484	$ 32,912	$ 9,682	$ 33,102

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held due to increases in cash flows expected to be collected and recognized over the remaining life of the security.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27340-111563

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