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Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) (USD $) In Thousands, unless otherwise specified |  |  | 9 Months Ended
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Sep. 30, 2014 | Dec. 31, 2013 | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL IV [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL V [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL VII [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL VIII [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL IX [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL X [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL XII [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL XIII [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL XIV [Member] Bank | Sep. 30, 2014 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] MMCap I [Member] Bank
Impairment Of Investment Securities [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Book Value |  |  | $ 41,971 | $ 1,830 | $ 59 | $ 2,723 | $ 1,956 | $ 2,331 | $ 1,469 | $ 5,484 | $ 12,403 | $ 13,277 | $ 439
Securities available for sale, at fair value | 1,332,774 | 1,318,365 | 29,456 | 1,327 | 127 | 2,864 | 1,332 | 1,453 | 1,508 | 3,455 | 8,536 | 8,477 | 377
Unrealized Gain (Loss) |  |  | $ (12,515) | $ (503) | $ 68 | $ 141 | $ (624) | $ (878) | $ 39 | $ (2,029) | $ (3,867) | $ (4,800) | $ (62)
Debt Instrument, Credit Rating |  |  |  | B1/BB | C/- | Ca/- | C/C | B3/C | Caa1/C | B3/C | Caa1/C | Caa1/C | Ca/C
Number of Banks (in banks) |  |  |  | 6 | 3 | 14 | 29 | 40 | 45 | 66 | 58 | 56 | 11
Deferrals and Defaults as a % of Current Collateral |  |  |  | 18.05% | 100.00% | 54.14% | 59.12% | 26.45% | 31.95% | 25.53% | 20.94% | 27.42% | 59.24%
Excess Subordination as a % of Current Performing Collateral |  |  |  | 41.28% | 0.00% | 0.00% | 0.00% | 2.23% | 0.00% | 0.00% | 23.85% | 43.02% | 19.70%

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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- Definition Amount of unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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