Investment Securities (Details 4) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Securities Available for Sale
One year or less	$ 184,752
Over one year through five years	2,623,871
Over five years through ten years	342,984
Over ten years	198,647
Fair Value	3,350,254
Weighted Average Yield, one year or less	1.89%
Weighted Average Yield, over one year through five years	2.94%
Weighted Average Yield, over five years through ten years	4.02%
Weighted Average Yield, over ten years	4.49%
Weighted Average Yield, Total	3.09%
Amortized Cost	3,267,600
Weighted-Average Yield	3.09%
Weighted-Average Maturity	4.14
Securities Held to Maturity
One year or less	30,791
Over one year through five years	14,425
Over five years through ten years	5,657
Over ten years	34,239
Fair Value	85,112
Weighted Average Yield, one year or less	3.33%
Weighted Average Yield, over one year through five years	3.37%
Weighted Average Yield, over five years through ten years	3.37%
Weighted Average Yield, over ten years	7.27%
Weighted Average Yield, Total	4.93%
Amortized Cost	82,764
Weighted Average Yield	4.93%
Weighted-Average Maturity	6.86
U.S. government agency debentures [Member]
Securities Available for Sale
One year or less	123,069
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	123,069
Amortized Cost	122,711
Weighted-Average Yield	0.78%
Weighted-Average Maturity	0.61
U.S. States and political subdivisions [Member]
Securities Available for Sale
One year or less	8,062
Over one year through five years	17,845
Over five years through ten years	177,411
Over ten years	154,413
Fair Value	357,731
Amortized Cost	334,916
Weighted-Average Yield	5.65%
Weighted-Average Maturity	9.85
Securities Held to Maturity
One year or less	30,791
Over one year through five years	14,425
Over five years through ten years	5,657
Over ten years	34,239
Fair Value	85,112
Amortized Cost	82,764
Weighted Average Yield	4.93%
Weighted-Average Maturity	6.86
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	2,758
Over one year through five years	1,442,442
Over five years through ten years	15,143
Over ten years	0
Fair Value	1,460,343
Amortized Cost	1,407,345
Weighted-Average Yield	3.36%
Weighted-Average Maturity	3.45
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	50,863
Over one year through five years	1,086,972
Over five years through ten years	0
Over ten years	0
Fair Value	1,137,835
Amortized Cost	1,115,832
Weighted-Average Yield	2.51%
Weighted-Average Maturity	2.64
Non-agency [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	16,094
Over five years through ten years	27,213
Over ten years	0
Fair Value	43,307
Amortized Cost	43,225
Weighted-Average Yield	0.77%
Weighted-Average Maturity	5.54
Commercial Mortgage Backed Securities [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	39,541
Over five years through ten years	89,586
Over ten years	0
Fair Value	129,127
Amortized Cost	127,624
Weighted-Average Yield	2.71%
Weighted-Average Maturity	6.52
Corporate debt securities [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	20,977
Over five years through ten years	33,631
Over ten years	44,234
Fair Value	98,842
Amortized Cost	$ 115,947
Weighted-Average Yield	1.67%
Weighted-Average Maturity	11.06