Significant Inputs Considered in Determining the Measurement of Credit Losses Recognized in Earnings for Securities (Detail)	3 Months Ended
Mar. 31, 2013
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Current default rate	6.00%
Prepayment rate	7.00%
Inputs Considered In Determining Measurement Of Credit Losses Loss Severity	61.00%
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Current default rate	9.00%
Prepayment rate	8.00%
Inputs Considered In Determining Measurement Of Credit Losses Loss Severity	74.00%

This item represents the default rate of the underlying assets in the security that was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8A

-Subparagraph a.1.

-URI http://asc.fasb.org/extlink&oid=27724398&loc=SL6284381-111563

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration