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Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 USD ($) Bank | Dec. 31, 2016 USD ($)
Impairment Of Investment Securities [Line Items] |  |
Securities available for sale, at fair value | $ 778,644 | $ 778,612
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 7,051 | 7,076
Unrealized Gain (Loss) | 13,282 | $ 18,546
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | 40,594 |
Securities available for sale, at fair value | 34,629 |
Unrealized Gain (Loss) | 5,965 |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | 1,820 |
Securities available for sale, at fair value | 1,393 |
Unrealized Gain (Loss) | $ 427 |
Debt Instrument, Credit Rating | Ba1/BB |
Number of Banks (in banks) | Bank | 6 |
Deferrals and Defaults as a % of Current Collateral | 18.05% |
Excess Subordination as a % of Current Performing Collateral | 65.06% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VIII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 2,013 |
Securities available for sale, at fair value | 2,215 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 202 |
Debt Instrument, Credit Rating | C/C |
Number of Banks (in banks) | Bank | 26 |
Deferrals and Defaults as a % of Current Collateral | 38.52% |
Excess Subordination as a % of Current Performing Collateral | 0.00% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IX [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 2,439 |
Securities available for sale, at fair value | 2,023 |
Unrealized Gain (Loss) | $ 416 |
Debt Instrument, Credit Rating | B1/C |
Number of Banks (in banks) | Bank | 37 |
Deferrals and Defaults as a % of Current Collateral | 27.83% |
Excess Subordination as a % of Current Performing Collateral | 10.00% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 1,831 |
Securities available for sale, at fair value | 2,062 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 231 |
Debt Instrument, Credit Rating | Caa1/C |
Number of Banks (in banks) | Bank | 42 |
Deferrals and Defaults as a % of Current Collateral | 30.10% |
Excess Subordination as a % of Current Performing Collateral | 2.06% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 6,044 |
Securities available for sale, at fair value | 5,064 |
Unrealized Gain (Loss) | $ 980 |
Debt Instrument, Credit Rating | B3/C |
Number of Banks (in banks) | Bank | 63 |
Deferrals and Defaults as a % of Current Collateral | 23.26% |
Excess Subordination as a % of Current Performing Collateral | 0.00% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 13,131 |
Securities available for sale, at fair value | 11,292 |
Unrealized Gain (Loss) | $ 1,839 |
Debt Instrument, Credit Rating | Ba1/CCC |
Number of Banks (in banks) | Bank | 51 |
Deferrals and Defaults as a % of Current Collateral | 8.88% |
Excess Subordination as a % of Current Performing Collateral | 48.56% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 13,101 |
Securities available for sale, at fair value | 10,282 |
Unrealized Gain (Loss) | $ 2,819 |
Debt Instrument, Credit Rating | Ba2/CCC |
Number of Banks (in banks) | Bank | 49 |
Deferrals and Defaults as a % of Current Collateral | 12.95% |
Excess Subordination as a % of Current Performing Collateral | 40.28% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 215 |
Securities available for sale, at fair value | 298 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 83 |
Debt Instrument, Credit Rating | Ca/C |
Number of Banks (in banks) | Bank | 8 |
Deferrals and Defaults as a % of Current Collateral | 58.11% |
Excess Subordination as a % of Current Performing Collateral | 58.72% |

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