Securities - Roll-Forward of Other-Than-Temporary Impairment Amount Related to Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Marketable Securities [Abstract]
Balance of credit losses on debt securities for which a portion of other-than-temporary impairment was recognized in earnings, beginning of period	$ 4,054	$ 4,054	$ 4,054	$ 4,054
Additional credit loss for which other-than-temporary impairment was not previously recognized	0	0	0	0
Additional credit loss for which other-than-temporary impairment was previously recognized	0	0	0	0
Balance of credit losses on debt securities for which a portion of other-than-temporary impairment was recognized in earnings, end of period	$ 4,054	$ 4,054	$ 4,054	$ 4,054

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This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (e)

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

+ Details

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- Definition

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which no such other than temporary impairment (OTTI) was previously recognized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8

-Subparagraph (b)

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

+ Details

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- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 8

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

+ Details

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