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Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2017 USD ($) Bank | Dec. 31, 2016 USD ($)
Impairment Of Investment Securities [Line Items] |  |
Securities available for sale, at fair value | $ 832,754 | $ 778,612
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 7,242 | 7,076
Unrealized Gain (Loss) | 16,821 | $ 18,546
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | 40,165 |
Securities available for sale, at fair value | 33,741 |
Unrealized Gain (Loss) | 6,424 |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | 1,827 |
Securities available for sale, at fair value | 1,366 |
Unrealized Gain (Loss) | $ 461 |
Debt Instrument, Credit Rating | B1/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 | 61.36% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VIII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 1,955 |
Securities available for sale, at fair value | 2,142 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 187 |
Debt Instrument, Credit Rating | C/C |
Number of Banks (in banks) | Bank | 27 |
Deferrals and Defaults as a % of Current Collateral | 40.34% |
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 | $ 2,421 |
Securities available for sale, at fair value | 1,971 |
Unrealized Gain (Loss) | $ 450 |
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 | 10.19% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 1,769 |
Securities available for sale, at fair value | 2,024 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 255 |
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 | 2.11% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 5,940 |
Securities available for sale, at fair value | 4,903 |
Unrealized Gain (Loss) | $ 1,037 |
Debt Instrument, Credit Rating | B3/C |
Number of Banks (in banks) | Bank | 64 |
Deferrals and Defaults as a % of Current Collateral | 24.09% |
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 | $ 13,010 |
Securities available for sale, at fair value | 11,009 |
Unrealized Gain (Loss) | $ 2,001 |
Debt Instrument, Credit Rating | Ba3/CCC |
Number of Banks (in banks) | Bank | 53 |
Deferrals and Defaults as a % of Current Collateral | 10.01% |
Excess Subordination as a % of Current Performing Collateral | 55.04% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 13,030 |
Securities available for sale, at fair value | 10,025 |
Unrealized Gain (Loss) | $ 3,005 |
Debt Instrument, Credit Rating | Ba2/CCC |
Number of Banks (in banks) | Bank | 52 |
Deferrals and Defaults as a % of Current Collateral | 12.87% |
Excess Subordination as a % of Current Performing Collateral | 38.83% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 213 |
Securities available for sale, at fair value | 301 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 88 |
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 | 85.00% |

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