Securities (Trust Preferred Securities) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Schedule Of Securities [Line Items]
TPS, Current Par Value	$ 105,294
TPS, Amortized Cost	43,559
TPS, Fair Value	30,806
TPS, Unrealized Gain (Loss)	(12,753)
TPS, Number of Issuers Currently Performing	893
Single Issuer TPS, Fair Value	6,999
Fair Value	23,807
Pooled TPS P1 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,500
Amortized Cost	2,491
Fair Value	1,103
Unrealized Gain (Loss)	(1,388)
Number of Issuers Currently Performing	42
Actual Defaults (as a percent of original collateral)	22.00%
Actual Deferrals (as a percent of original collateral)	12.00%
Projected Recovery Rates on Current Deferrals	46.00%	[1]
Expected Defaults	17.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P2 [Member]
Schedule Of Securities [Line Items]
Current Par Value	4,889
Amortized Cost	2,972
Fair Value	972
Unrealized Gain (Loss)	(2,000)
Number of Issuers Currently Performing	42
Actual Defaults (as a percent of original collateral)	17.00%
Actual Deferrals (as a percent of original collateral)	14.00%
Projected Recovery Rates on Current Deferrals	38.00%	[1]
Expected Defaults	15.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P3 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,561
Amortized Cost	4,260
Fair Value	1,292
Unrealized Gain (Loss)	(2,968)
Number of Issuers Currently Performing	47
Actual Defaults (as a percent of original collateral)	13.00%
Actual Deferrals (as a percent of original collateral)	9.00%
Projected Recovery Rates on Current Deferrals	31.00%	[1]
Expected Defaults	16.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P4 [Member]
Schedule Of Securities [Line Items]
Current Par Value	3,994
Amortized Cost	3,039
Fair Value	943
Unrealized Gain (Loss)	(2,096)
Number of Issuers Currently Performing	52
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	6.00%
Projected Recovery Rates on Current Deferrals	37.00%	[1]
Expected Defaults	16.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P5 [Member]
Schedule Of Securities [Line Items]
Current Par Value	2,000
Amortized Cost	739
Fair Value	327
Unrealized Gain (Loss)	(412)
Number of Issuers Currently Performing	15
Actual Defaults (as a percent of original collateral)	29.00%
Actual Deferrals (as a percent of original collateral)	10.00%
Projected Recovery Rates on Current Deferrals	46.00%	[1]
Expected Defaults	11.00%	[2]
Class	B3
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P6 [Member]
Schedule Of Securities [Line Items]
Current Par Value	3,028
Amortized Cost	2,419
Fair Value	826
Unrealized Gain (Loss)	(1,593)
Number of Issuers Currently Performing	49
Actual Defaults (as a percent of original collateral)	14.00%
Actual Deferrals (as a percent of original collateral)	21.00%
Projected Recovery Rates on Current Deferrals	44.00%	[1]
Expected Defaults	10.00%	[2]
Class	B1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P7 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,048
Amortized Cost	776
Fair Value	388
Unrealized Gain (Loss)	(388)
Number of Issuers Currently Performing	34
Actual Defaults (as a percent of original collateral)	14.00%
Actual Deferrals (as a percent of original collateral)	28.00%
Projected Recovery Rates on Current Deferrals	39.00%	[1]
Expected Defaults	13.00%	[2]
Class	C
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P8 [Member]
Schedule Of Securities [Line Items]
Current Par Value	2,011
Amortized Cost	788
Fair Value	185
Unrealized Gain (Loss)	(603)
Number of Issuers Currently Performing	43
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	12.00%
Projected Recovery Rates on Current Deferrals	36.00%	[1]
Expected Defaults	17.00%	[2]
Class	C
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P9 [Member]
Schedule Of Securities [Line Items]
Current Par Value	2,000
Amortized Cost	645
Fair Value	228
Unrealized Gain (Loss)	(417)
Number of Issuers Currently Performing	25
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	14.00%
Projected Recovery Rates on Current Deferrals	44.00%	[1]
Expected Defaults	11.00%	[2]
Class	A4L
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Total OTTI [Member]
Schedule Of Securities [Line Items]
Current Par Value	34,031
Amortized Cost	18,129
Fair Value	6,264
Unrealized Gain (Loss)	(11,865)
Number of Issuers Currently Performing	349
Actual Defaults (as a percent of original collateral)	17.00%
Actual Deferrals (as a percent of original collateral)	14.00%
Projected Recovery Rates on Current Deferrals	40.00%	[1]
Expected Defaults	15.00%	[2]
Pooled TPS P10 [Member]
Schedule Of Securities [Line Items]
Current Par Value	488
Amortized Cost	505
Fair Value	478
Unrealized Gain (Loss)	(27)
Number of Issuers Currently Performing	8
Actual Defaults (as a percent of original collateral)	15.00%
Actual Deferrals (as a percent of original collateral)	11.00%
Projected Recovery Rates on Current Deferrals	51.00%	[1]
Expected Defaults	11.00%	[2]
Class	SNR
Lowest Credit Ratings	A2
Excess Subordination (as a percent of current collateral)	103.71%	[3]
Pooled TPS P11 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,219
Amortized Cost	1,012
Fair Value	1,047
Unrealized Gain (Loss)	35
Number of Issuers Currently Performing	42
Actual Defaults (as a percent of original collateral)	22.00%
Actual Deferrals (as a percent of original collateral)	12.00%
Projected Recovery Rates on Current Deferrals	46.00%	[1]
Expected Defaults	17.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P12 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,000
Amortized Cost	2,124
Fair Value	1,896
Unrealized Gain (Loss)	(228)
Number of Issuers Currently Performing	43
Actual Defaults (as a percent of original collateral)	17.00%
Actual Deferrals (as a percent of original collateral)	14.00%
Projected Recovery Rates on Current Deferrals	38.00%	[1]
Expected Defaults	15.00%	[2]
Class	A2A
Lowest Credit Ratings	B+
Excess Subordination (as a percent of current collateral)	44.37%	[3]
Pooled TPS P13 [Member]
Schedule Of Securities [Line Items]
Current Par Value	4,781
Amortized Cost	1,225
Fair Value	1,111
Unrealized Gain (Loss)	(114)
Number of Issuers Currently Performing	47
Actual Defaults (as a percent of original collateral)	13.00%
Actual Deferrals (as a percent of original collateral)	9.00%
Projected Recovery Rates on Current Deferrals	31.00%	[1]
Expected Defaults	16.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P14 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,260
Amortized Cost	1,179
Fair Value	1,242
Unrealized Gain (Loss)	63
Number of Issuers Currently Performing	52
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	6.00%
Projected Recovery Rates on Current Deferrals	37.00%	[1]
Expected Defaults	16.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P15 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,190
Amortized Cost	979
Fair Value	1,189
Unrealized Gain (Loss)	210
Number of Issuers Currently Performing	59
Actual Defaults (as a percent of original collateral)	15.00%
Actual Deferrals (as a percent of original collateral)	12.00%
Projected Recovery Rates on Current Deferrals	35.00%	[1]
Expected Defaults	17.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	4.20%	[3]
Pooled TPS P16 [Member]
Schedule Of Securities [Line Items]
Current Par Value	3,206
Amortized Cost	370
Fair Value	537
Unrealized Gain (Loss)	167
Number of Issuers Currently Performing	44
Actual Defaults (as a percent of original collateral)	19.00%
Actual Deferrals (as a percent of original collateral)	6.00%
Projected Recovery Rates on Current Deferrals	27.00%	[1]
Expected Defaults	18.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P17 [Member]
Schedule Of Securities [Line Items]
Current Par Value	3,339
Amortized Cost	601
Fair Value	638
Unrealized Gain (Loss)	37
Number of Issuers Currently Performing	35
Actual Defaults (as a percent of original collateral)	15.00%
Actual Deferrals (as a percent of original collateral)	13.00%
Projected Recovery Rates on Current Deferrals	26.00%	[1]
Expected Defaults	16.00%	[2]
Class	C
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P18 [Member]
Schedule Of Securities [Line Items]
Current Par Value	2,069
Amortized Cost	633
Fair Value	541
Unrealized Gain (Loss)	(92)
Number of Issuers Currently Performing	33
Actual Defaults (as a percent of original collateral)	13.00%
Actual Deferrals (as a percent of original collateral)	24.00%
Projected Recovery Rates on Current Deferrals	34.00%	[1]
Expected Defaults	14.00%	[2]
Class	B
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	17.67%	[3]
Pooled TPS P19 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,000
Amortized Cost	2,199
Fair Value	2,540
Unrealized Gain (Loss)	341
Number of Issuers Currently Performing	22
Actual Defaults (as a percent of original collateral)	0.00%
Actual Deferrals (as a percent of original collateral)	4.00%
Projected Recovery Rates on Current Deferrals	10.00%	[1]
Expected Defaults	13.00%	[2]
Class	B2
Lowest Credit Ratings	CCC
Excess Subordination (as a percent of current collateral)	42.23%	[3]
Pooled TPS P20 [Member]
Schedule Of Securities [Line Items]
Current Par Value	4,051
Amortized Cost	939
Fair Value	963
Unrealized Gain (Loss)	24
Number of Issuers Currently Performing	40
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	12.00%
Projected Recovery Rates on Current Deferrals	36.00%	[1]
Expected Defaults	17.00%	[2]
Class	B
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	11.80%	[3]
Pooled TPS P21 [Member]
Schedule Of Securities [Line Items]
Current Par Value	3,523
Amortized Cost	2,094
Fair Value	2,015
Unrealized Gain (Loss)	(79)
Number of Issuers Currently Performing	47
Actual Defaults (as a percent of original collateral)	21.00%
Actual Deferrals (as a percent of original collateral)	6.00%
Projected Recovery Rates on Current Deferrals	40.00%	[1]
Expected Defaults	15.00%	[2]
Class	A1
Lowest Credit Ratings	BB-
Excess Subordination (as a percent of current collateral)	51.55%	[3]
Pooled TPS P22 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,000
Amortized Cost	1,271
Fair Value	1,044
Unrealized Gain (Loss)	(227)
Number of Issuers Currently Performing	15
Actual Defaults (as a percent of original collateral)	18.00%
Actual Deferrals (as a percent of original collateral)	6.00%
Projected Recovery Rates on Current Deferrals	44.00%	[1]
Expected Defaults	11.00%	[2]
Class	B
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P23 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,531
Amortized Cost	1,291
Fair Value	1,111
Unrealized Gain (Loss)	(180)
Number of Issuers Currently Performing	26
Actual Defaults (as a percent of original collateral)	15.00%
Actual Deferrals (as a percent of original collateral)	12.00%
Projected Recovery Rates on Current Deferrals	36.00%	[1]
Expected Defaults	10.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Pooled TPS P24 [Member]
Schedule Of Securities [Line Items]
Current Par Value	5,606
Amortized Cost	1,180
Fair Value	1,191
Unrealized Gain (Loss)	11
Number of Issuers Currently Performing	26
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	9.00%
Projected Recovery Rates on Current Deferrals	43.00%	[1]
Expected Defaults	11.00%	[2]
Class	C1
Lowest Credit Ratings	C
Excess Subordination (as a percent of current collateral)	0.00%	[3]
Total Not OTTI [Member]
Schedule Of Securities [Line Items]
Current Par Value	63,263
Amortized Cost	17,602
Fair Value	17,543
Unrealized Gain (Loss)	(59)
Number of Issuers Currently Performing	539
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	10.00%
Projected Recovery Rates on Current Deferrals	36.00%	[1]
Expected Defaults	15.00%	[2]
Total Pooled TPS [Member]
Schedule Of Securities [Line Items]
Current Par Value	97,294
Amortized Cost	35,731
Fair Value	23,807
Unrealized Gain (Loss)	(11,924)
Number of Issuers Currently Performing	888
Actual Defaults (as a percent of original collateral)	16.00%
Actual Deferrals (as a percent of original collateral)	11.00%
Projected Recovery Rates on Current Deferrals	38.00%	[1]
Expected Defaults	15.00%	[2]
Single Issuer TPS S1 [Member]
Schedule Of Securities [Line Items]
Single Issuer TPS, Current Par Value	2,000
Single Issuer TPS, Amortized Cost	1,953
Single Issuer TPS, Fair Value	1,533
Single Issuer TPS, Unrealized Gain (Loss)	(420)
Lowest Credit Ratings	BB
Single Issuer TPS, Number of Issuers Currently Performing	1
Single Issuer TPS S2 [Member]
Schedule Of Securities [Line Items]
Single Issuer TPS, Current Par Value	2,000
Single Issuer TPS, Amortized Cost	1,921
Single Issuer TPS, Fair Value	1,664
Single Issuer TPS, Unrealized Gain (Loss)	(257)
Lowest Credit Ratings	BBB
Single Issuer TPS, Number of Issuers Currently Performing	1
Single Issuer TPS S3 [Member]
Schedule Of Securities [Line Items]
Single Issuer TPS, Current Par Value	1,000
Single Issuer TPS, Amortized Cost	955
Single Issuer TPS, Fair Value	1,033
Single Issuer TPS, Unrealized Gain (Loss)	78
Lowest Credit Ratings	BB+
Single Issuer TPS, Number of Issuers Currently Performing	1
Single Issuer TPS S4 [Member]
Schedule Of Securities [Line Items]
Single Issuer TPS, Current Par Value	2,000
Single Issuer TPS, Amortized Cost	2,000
Single Issuer TPS, Fair Value	1,985
Single Issuer TPS, Unrealized Gain (Loss)	(15)
Lowest Credit Ratings	BB+
Single Issuer TPS, Number of Issuers Currently Performing	1
Single Issuer TPS S5 [Member]
Schedule Of Securities [Line Items]
Single Issuer TPS, Current Par Value	1,000
Single Issuer TPS, Amortized Cost	999
Single Issuer TPS, Fair Value	784
Single Issuer TPS, Unrealized Gain (Loss)	(215)
Lowest Credit Ratings	BB
Single Issuer TPS, Number of Issuers Currently Performing	1
Single Issuer TPS [Member]
Schedule Of Securities [Line Items]
Single Issuer TPS, Current Par Value	8,000
Single Issuer TPS, Amortized Cost	7,828
Single Issuer TPS, Fair Value	6,999
Single Issuer TPS, Unrealized Gain (Loss)	$ (829)
Single Issuer TPS, Number of Issuers Currently Performing	5

[1] Some current deferrals are expected to cure at rates varying from 10% to 90% after five years.

[2] Expected future defaults as a percent of remaining performing collateral.

[3] Excess subordination represents the additional defaults in excess of both current and projected defaults that the CDO can absorb before the bond experiences any credit impairment.