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Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 USD ($) Bank | Dec. 31, 2015 USD ($)
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 790,082 | $ 891,111
Estimated Fair Value of Available for Sale | 778,612 | $ 886,560
Mezzanine [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | 39,989 |
Estimated Fair Value of Available for Sale | 33,292 |
Unrealized Gain (Loss) | (6,697) |
Mezzanine [Member] | Pre TSL IV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | 1,830 |
Estimated Fair Value of Available for Sale | 1,360 |
Unrealized Gain (Loss) | $ (470) |
Debt Instrument, Credit Rating | B1/BB |
Number of Banks | Bank | 6 |
Deferrals and Defaults as a % of Current Collateral | 18.05% |
Excess Subordination as a % of Current Performing Collateral | 59.78% |
Mezzanine [Member] | Pre TSL VII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 3,100 |
Mezzanine [Member] | Pre TSL VIII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | 1,963 |
Estimated Fair Value of Available for Sale | 2,053 |
Unrealized Gain (Loss) | $ 90 |
Debt Instrument, Credit Rating | C/C |
Number of Banks | Bank | 28 |
Deferrals and Defaults as a % of Current Collateral | 44.37% |
Excess Subordination as a % of Current Performing Collateral | 0.00% |
Mezzanine [Member] | Pre TSL IX [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 2,412 |
Estimated Fair Value of Available for Sale | 1,952 |
Unrealized Gain (Loss) | $ (460) |
Debt Instrument, Credit Rating | B1/C |
Number of Banks | Bank | 37 |
Deferrals and Defaults as a % of Current Collateral | 27.83% |
Excess Subordination as a % of Current Performing Collateral | 12.79% |
Mezzanine [Member] | Pre TSL X [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 1,738 |
Estimated Fair Value of Available for Sale | 1,986 |
Unrealized Gain (Loss) | $ 248 |
Debt Instrument, Credit Rating | Caa1/C |
Number of Banks | Bank | 42 |
Deferrals and Defaults as a % of Current Collateral | 31.58% |
Excess Subordination as a % of Current Performing Collateral | 2.17% |
Mezzanine [Member] | Pre TSL XII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 5,890 |
Estimated Fair Value of Available for Sale | 4,817 |
Unrealized Gain (Loss) | $ (1,073) |
Debt Instrument, Credit Rating | B3/C |
Number of Banks | Bank | 64 |
Deferrals and Defaults as a % of Current Collateral | 24.54% |
Excess Subordination as a % of Current Performing Collateral | 0.00% |
Mezzanine [Member] | Pre TSL XIII [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 12,949 |
Estimated Fair Value of Available for Sale | 10,900 |
Unrealized Gain (Loss) | $ (2,049) |
Debt Instrument, Credit Rating | Ba3/C |
Number of Banks | Bank | 54 |
Deferrals and Defaults as a % of Current Collateral | 11.21% |
Excess Subordination as a % of Current Performing Collateral | 55.77% |
Mezzanine [Member] | Pre TSL XIV [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 12,995 |
Estimated Fair Value of Available for Sale | 9,923 |
Unrealized Gain (Loss) | $ (3,072) |
Debt Instrument, Credit Rating | B1/CC |
Number of Banks | Bank | 52 |
Deferrals and Defaults as a % of Current Collateral | 12.78% |
Excess Subordination as a % of Current Performing Collateral | 31.90% |
Mezzanine [Member] | MMCap I [Member] |  |
Impairment Of Investment Securities [Line Items] |  |
Amortized Cost | $ 212 |
Estimated Fair Value of Available for Sale | 301 |
Unrealized Gain (Loss) | $ 89 |
Debt Instrument, Credit Rating | Ca/C |
Number of Banks | Bank | 8 |
Deferrals and Defaults as a % of Current Collateral | 58.11% |
Excess Subordination as a % of Current Performing Collateral | 80.31% |

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