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Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands | 6 Months Ended |
--- | --- | ---
Jun. 30, 2017 USD ($) Bank | Dec. 31, 2016 USD ($)
Impairment Of Investment Securities [Line Items] |  |
Securities available for sale, at fair value | $ 786,246 | $ 778,612
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | 7,434 | 7,076
Unrealized Gain (Loss) | 15,263 | $ 18,546
Pooled Trust Preferred Collateralized Debt Obligations [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | 40,378 |
Securities available for sale, at fair value | 33,648 |
Unrealized Gain (Loss) | 6,730 |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL IV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | 1,823 |
Securities available for sale, at fair value | 1,361 |
Unrealized Gain (Loss) | $ 462 |
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 | 60.51% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL VIII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 1,983 |
Securities available for sale, at fair value | 2,139 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 156 |
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 | $ 2,430 |
Securities available for sale, at fair value | 1,965 |
Unrealized Gain (Loss) | $ 465 |
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 | 11.71% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL X [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 1,801 |
Securities available for sale, at fair value | 2,016 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 215 |
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 | 1.97% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 5,991 |
Securities available for sale, at fair value | 4,913 |
Unrealized Gain (Loss) | $ 1,078 |
Debt Instrument, Credit Rating | B3/C |
Number of Banks (in banks) | Bank | 64 |
Deferrals and Defaults as a % of Current Collateral | 24.13% |
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 | $ 13,070 |
Securities available for sale, at fair value | 10,965 |
Unrealized Gain (Loss) | $ 2,105 |
Debt Instrument, Credit Rating | Ba1/CCC |
Number of Banks (in banks) | Bank | 52 |
Deferrals and Defaults as a % of Current Collateral | 8.02% |
Excess Subordination as a % of Current Performing Collateral | 45.06% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | Pre TSL XIV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 13,066 |
Securities available for sale, at fair value | 9,983 |
Unrealized Gain (Loss) | $ 3,083 |
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 | 40.25% |
Pooled Trust Preferred Collateralized Debt Obligations [Member] | Mezzanine [Member] | MMCap I [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Book Value | $ 214 |
Securities available for sale, at fair value | 306 |
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax | $ 92 |
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 | 83.52% |

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