Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) (USD $) In Thousands, unless otherwise specified				12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior [Member] Pre TSL I [Member]	Dec. 31, 2012 Senior [Member] MMCap I [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL IV [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL V [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL VII [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL VIII [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL IX [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL X [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL XII [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL XIII [Member]	Dec. 31, 2012 Mezzanine [Member] Pre TSL XIV [Member]	Dec. 31, 2012 Mezzanine [Member] MMCap I [Member]	Dec. 31, 2012 Mezzanine [Member] MM Comm IX [Member]	Dec. 31, 2012 Preferred Collateralized Debt Obligations Total [Member] Moody's, C Rating [Member] Mezzanine [Member] Pre TSL V [Member] Bank	Dec. 31, 2012 Fitch, A Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Aa3 Rating [Member] Senior [Member] Pre TSL I [Member] Bank	Dec. 31, 2012 Fitch, A Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, A3 Rating [Member] Senior [Member] MMCap I [Member] Bank	Dec. 31, 2012 Fitch, CCC Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Caa2 Rating [Member] Mezzanine [Member] Pre TSL IV [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, C Rating [Member] Mezzanine [Member] Pre TSL VIII [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] Pre TSL VII [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] Pre TSL IX [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] Pre TSL X [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] Pre TSL XII [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] Pre TSL XIII [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] Pre TSL XIV [Member] Bank	Dec. 31, 2012 Fitch, C Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] MMCap I [Member] Bank	Dec. 31, 2012 Fitch, CC Rating [Member] Preferred Collateralized Debt Obligations Total [Member] Moody's, Ca Rating [Member] Mezzanine [Member] MM Comm IX [Member] Bank
Impairment Of Investment Securities [Line Items]
Book Value	$ 51,866		$ 1,009	$ 1,220	$ 1,830	$ 54	$ 3,654	$ 1,833	$ 2,268	$ 1,388	$ 5,508	$ 12,571	$ 13,188	$ 867	$ 6,476
Fair Value	1,171,303	1,142,776	1,005	1,193	1,111	57	3,326	1,007	943	1,165	2,531	4,456	4,783	466	1,330
Unrealized Gain (Loss)	$ (28,493)		$ (4)	$ (27)	$ (719)	$ 3	$ (328)	$ (826)	$ (1,325)	$ (223)	$ (2,977)	$ (8,115)	$ (8,405)	$ (401)	$ (5,146)
Number of Banks																3	17	17	6	32	16	46	50	71	63	61	17	29
Deferrals and Defaults as a % of Current Collateral																100.00%	33.33%	50.26%	27.07%	52.99%	48.92%	25.50%	35.24%	35.35%	36.87%	38.97%	50.26%	42.41%
Excess Subordination as a % of Current Performing Collateral																0.00%	159.27%	573.29%	91.00%	0.00%	0.00%	13.32%	0.00%	0.00%	6.48%	29.37%	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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