Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($) Bank	Dec. 31, 2014 USD ($)
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 891,111	$ 1,317,318
Estimated Fair Value of Available for Sale	886,560	$ 1,309,819
Mezzanine [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	42,239
Estimated Fair Value of Available for Sale	35,658
Unrealized Gain (Loss)	(6,581)
Mezzanine [Member] \| Pre TSL IV [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	1,830
Estimated Fair Value of Available for Sale	1,336
Unrealized Gain (Loss)	$ (494)
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	59.91%
Mezzanine [Member] \| Pre TSL VII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 2,963
Estimated Fair Value of Available for Sale	3,484
Unrealized Gain (Loss)	$ 521
Debt Instrument, Credit Rating	Ca/-
Number of Banks \| Bank	14
Deferrals and Defaults as a % of Current Collateral	49.68%
Excess Subordination as a % of Current Performing Collateral	0.00%
Mezzanine [Member] \| Pre TSL VIII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 2,000
Estimated Fair Value of Available for Sale	1,863
Unrealized Gain (Loss)	$ (137)
Debt Instrument, Credit Rating	C/C
Number of Banks \| Bank	29
Deferrals and Defaults as a % of Current Collateral	56.74%
Excess Subordination as a % of Current Performing Collateral	0.00%
Mezzanine [Member] \| Pre TSL IX [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 2,376
Estimated Fair Value of Available for Sale	1,805
Unrealized Gain (Loss)	$ (571)
Debt Instrument, Credit Rating	B1/C
Number of Banks \| Bank	38
Deferrals and Defaults as a % of Current Collateral	29.80%
Excess Subordination as a % of Current Performing Collateral	9.90%
Mezzanine [Member] \| Pre TSL X [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 1,613
Estimated Fair Value of Available for Sale	1,915
Unrealized Gain (Loss)	$ 302
Debt Instrument, Credit Rating	Caa1/C
Number of Banks \| Bank	43
Deferrals and Defaults as a % of Current Collateral	30.66%
Excess Subordination as a % of Current Performing Collateral	0.00%
Mezzanine [Member] \| Pre TSL XII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 5,688
Estimated Fair Value of Available for Sale	4,585
Unrealized Gain (Loss)	$ (1,103)
Debt Instrument, Credit Rating	B3/C
Number of Banks \| Bank	66
Deferrals and Defaults as a % of Current Collateral	23.07%
Excess Subordination as a % of Current Performing Collateral	0.00%
Mezzanine [Member] \| Pre TSL XIII [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 12,706
Estimated Fair Value of Available for Sale	10,660
Unrealized Gain (Loss)	$ (2,046)
Debt Instrument, Credit Rating	Ba3/C
Number of Banks \| Bank	56
Deferrals and Defaults as a % of Current Collateral	11.08%
Excess Subordination as a % of Current Performing Collateral	37.45%
Mezzanine [Member] \| Pre TSL XIV [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 12,854
Estimated Fair Value of Available for Sale	9,708
Unrealized Gain (Loss)	$ (3,146)
Debt Instrument, Credit Rating	B1/CC
Number of Banks \| Bank	56
Deferrals and Defaults as a % of Current Collateral	19.72%
Excess Subordination as a % of Current Performing Collateral	47.01%
Mezzanine [Member] \| MMCap I [Member]
Impairment Of Investment Securities [Line Items]
Amortized Cost	$ 209
Estimated Fair Value of Available for Sale	302
Unrealized Gain (Loss)	$ 93
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	83.61%

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Excess subordination as a percentage of current performing collateral.

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Impairment Of Investment Securities [Line Items]

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- Definition

Pooled trust preferred collateralized debt obligations in number of banks.

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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

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-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

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Amount before tax of unrealized gain (loss) in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Description of the credit rating indicative of likelihood of repayment of the debt instrument given by a credit rating agency (for example, Standard and Poor's, Moody's, Fitch).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

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