Investment Securities (Maturities Table) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Securities Available for Sale
One year or less	$ 55,888
Over one year through five years	2,144,204
Over five years through ten years	965,488
Over ten years	84,302
Fair Value	3,249,882
Weighted Average Yield, one year or less	3.51%
Weighted Average Yield, over one year through five years	2.30%
Weighted Average Yield, over five years through ten years	2.63%
Weighted Average Yield, over ten years	2.18%
Weighted Average Yield, Total	2.42%
Amortized Cost	3,279,732
Weighted-Average Yield	2.42%
Weighted-Average Maturity	4.80
Securities Held to Maturity
One year or less	47,561
Over one year through five years	1,464,821
Over five years through ten years	943,803
Over ten years	202,248
Held-to-maturity Securities, Fair Value	2,658,433	630,799	631,237
Weighted Average Yield, one year or less	1.38%
Weighted Average Yield, over one year through five years	1.66%
Weighted Average Yield, over five years through ten years	2.21%
Weighted Average Yield, over ten years	5.07%
Weighted Average Yield, Total	2.11%
Held-to-maturity	2,749,934	622,121	620,631
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	2,749,934	622,121	620,631
Weighted Average Yield	2.11%
Weighted-Average Maturity	5.68
US Government Agencies Debt Securities
Securities Held to Maturity
One year or less	0
Over one year through five years	0
Over five years through ten years	23,864
Over ten years	0
Held-to-maturity Securities, Fair Value	23,864
Held-to-maturity	23,864
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	25,000
Weighted Average Yield	1.43%
Weighted-Average Maturity	6.08
US Treasury Securities
Securities Held to Maturity
One year or less	0
Over one year through five years	5,005
Over five years through ten years	0
Over ten years	0
Held-to-maturity Securities, Fair Value	5,005
Held-to-maturity	5,005
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	5,000
Weighted Average Yield	0.25%
Weighted-Average Maturity	1.33
U.S. States and political subdivisions debt securities
Securities Available for Sale
One year or less	14,460
Over one year through five years	53,128
Over five years through ten years	171,184
Over ten years	33,452
Fair Value	272,224
Amortized Cost	267,470
Weighted-Average Yield	5.23%
Weighted-Average Maturity	6.98
Securities Held to Maturity
One year or less	47,561
Over one year through five years	47,157
Over five years through ten years	152,100
Over ten years	202,248
Held-to-maturity Securities, Fair Value	449,066
Held-to-maturity	449,066	275,061	269,020
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	453,230	270,005	262,091
Weighted Average Yield	4.54%
Weighted-Average Maturity	11.24
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities Available for Sale
One year or less	3,649
Over one year through five years	797,680
Over five years through ten years	198,046
Over ten years	0
Fair Value	999,375
Amortized Cost	983,255
Weighted-Average Yield	2.78%
Weighted-Average Maturity	4.10
Securities Held to Maturity
One year or less	0
Over one year through five years	137,350
Over five years through ten years	233,120
Over ten years	0
Held-to-maturity Securities, Fair Value	370,470
Held-to-maturity	370,470
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	377,980
Weighted Average Yield	1.87%
Weighted-Average Maturity	5.81
Commercial Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities Available for Sale
One year or less	17,085
Over one year through five years	5,109
Over five years through ten years	33,738
Over ten years	0
Fair Value	55,932
Amortized Cost	58,129
Weighted-Average Yield	2.10%
Weighted-Average Maturity	4.29
Securities Held to Maturity
One year or less	0
Over one year through five years	15,120
Over five years through ten years	34,046
Over ten years	0
Held-to-maturity Securities, Fair Value	49,166
Held-to-maturity	49,166	33,977	33,941
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	50,179	33,165	33,149
Weighted Average Yield	1.74%
Weighted-Average Maturity	5.81
Residential Collateralized Mortgage-Backed Securities Issued by US Government Sponsored Enterprises
Securities Available for Sale
One year or less	7,125
Over one year through five years	1,204,551
Over five years through ten years	294,030
Over ten years	0
Fair Value	1,505,706
Amortized Cost	1,538,991
Weighted-Average Yield	1.85%
Weighted-Average Maturity	4.26
Securities Held to Maturity
One year or less	0
Over one year through five years	1,088,688
Over five years through ten years	366,564
Over ten years	0
Held-to-maturity Securities, Fair Value	1,455,252
Held-to-maturity	1,455,252	124,080	129,661
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	1,523,792	123,563	129,265
Weighted Average Yield	1.57%
Weighted-Average Maturity	4.60
Residential Collateralized Mortgage-Backed Securities Issued by Non-US Government Agency
Securities Available for Sale
One year or less	1
Over one year through five years	8
Over five years through ten years	0
Over ten years	0
Fair Value	9
Amortized Cost	9
Weighted-Average Yield	3.68%
Weighted-Average Maturity	1.37
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises
Securities Available for Sale
One year or less	0
Over one year through five years	71,890
Over five years through ten years	25,264
Over ten years	0
Fair Value	97,154
Amortized Cost	98,440
Weighted-Average Yield	1.80%
Weighted-Average Maturity	4.37
Securities Held to Maturity
One year or less	0
Over one year through five years	97,014
Over five years through ten years	114,460
Over ten years	0
Held-to-maturity Securities, Fair Value	211,474
Held-to-maturity	211,474	99,696	100,015
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	220,410	98,924	98,961
Weighted Average Yield	2.26%
Weighted-Average Maturity	5.41
Collateralized Loan Obligations
Securities Available for Sale
One year or less	13,568
Over one year through five years	11,838
Over five years through ten years	243,226
Over ten years	0
Fair Value	268,632
Amortized Cost	271,856
Weighted-Average Yield	2.14%
Weighted-Average Maturity	6.37
Corporate debt securities
Securities Available for Sale
One year or less	0
Over one year through five years	0
Over five years through ten years	0
Over ten years	50,850
Fair Value	50,850
Amortized Cost	61,582
Weighted-Average Yield	0.97%
Weighted-Average Maturity	14.06
Securities Held to Maturity
One year or less	0
Over one year through five years	74,487
Over five years through ten years	19,649
Over ten years	0
Held-to-maturity Securities, Fair Value	94,136
Held-to-maturity	94,136	97,985	98,600
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 94,343	$ 96,464	$ 97,165
Weighted Average Yield	2.19%
Weighted-Average Maturity	4.29