Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) (USD $) In Thousands, unless otherwise specified				9 Months Ended
Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member]	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Senior [Member] Pre TSL I [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL IV [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL V [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL VII [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL VIII [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL IX [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL X [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL XII [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL XIII [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] Pre TSL XIV [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] MMCap I [Member] Bank	Sep. 30, 2013 Pooled Trust Preferred Collateralized Debt Obligations [Member] Mezzanine [Member] MM Comm IX [Member] Bank
Impairment Of Investment Securities [Line Items]
Book Value			$ 48,824	$ 2	$ 1,830	$ 57	$ 2,722	$ 1,927	$ 2,295	$ 1,367	$ 5,380	$ 12,468	$ 13,537	$ 644	$ 6,595
Estimated Fair Value	1,291,063	1,171,303	25,457	2	1,266	34	2,818	1,093	1,133	1,330	2,958	7,051	6,211	495	1,066
Unrealized Gain (Loss)			$ (23,367)	$ 0	$ (564)	$ (23)	$ 96	$ (834)	$ (1,162)	$ (37)	$ (2,422)	$ (5,417)	$ (7,326)	$ (149)	$ (5,529)
Debt Instrument, Credit Rating				Aa3/AAA	Caa2/B	C/-	Ca/C	C/C	Caa1/C	Caa3(Ca)/C	Caa3/C	Caa3(Ca)/C	Ca/C	Ca/C	Ca/D
Number of Banks (in banks)				9	6	3	15	30	44	47	69	61	59	11	27
Deferrals and Defaults as a % of Current Collateral				33.33%	18.05%	100.00%	52.80%	58.01%	27.04%	34.92%	30.17%	29.99%	37.00%	58.76%	44.41%
Excess Subordination as a % of Current Performing Collateral				0.00%	56.91%	0.00%	0.00%	0.00%	6.44%	0.00%	0.00%	16.38%	35.64%	0.00%	0.00%

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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