Investment Securities (Details 4) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012
Securities Available for Sale
One year or less	$ 121,174
Over one year through five years	2,625,817
Over five years through ten years	370,691
Over ten years	95,343
Fair Value	3,213,025
Weighted Average Yield, one year or less	3.22%
Weighted Average Yield, over one year through five years	2.72%
Weighted Average Yield, over five years through ten years	3.69%
Weighted Average Yield, over ten years	2.83%
Weighted Average Yield, Total	2.85%
Amortized Cost	3,132,098
Weighted-Average Yield	2.85%
Weighted-Average Maturity	3.87
Securities Held to Maturity
One year or less	41,042
Over one year through five years	14,567
Over five years through ten years	121,363
Over ten years	178,148
Fair Value	355,120
Weighted Average Yield, one year or less	1.54%
Weighted Average Yield, over one year through five years	4.48%
Weighted Average Yield, over five years through ten years	2.51%
Weighted Average Yield, over ten years	5.57%
Weighted Average Yield, Total	4.01%
Amortized Cost	352,221
Weighted Average Yield	4.01%
Weighted-Average Maturity	9.9600
US Government Agencies Debt Securities [Member]
Securities Available for Sale
One year or less	35,297
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	35,297
Amortized Cost	35,224
Weighted-Average Yield	0.73%
Weighted-Average Maturity	0.40
US States and Political Subdivisions Debt Securities [Member]
Securities Available for Sale
One year or less	15,897
Over one year through five years	27,984
Over five years through ten years	173,985
Over ten years	47,258
Fair Value	265,124
Amortized Cost	249,410
Weighted-Average Yield	5.36%
Weighted-Average Maturity	7.76
Securities Held to Maturity
One year or less	41,042
Over one year through five years	14,567
Over five years through ten years	22,318
Over ten years	178,148
Fair Value	256,075
Amortized Cost	253,161
Weighted Average Yield	5.58%
Weighted-Average Maturity	13.75
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	5,134
Over one year through five years	1,330,029
Over five years through ten years	47,650
Over ten years	0
Fair Value	1,382,813
Amortized Cost	1,326,601
Weighted-Average Yield	3.09%
Weighted-Average Maturity	3.25
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	0
Over five years through ten years	38,428
Over ten years	0
Fair Value	38,428
Amortized Cost	37,868
Weighted-Average Yield	1.70%
Weighted-Average Maturity	6.10
Residential Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	64,846
Over one year through five years	1,180,481
Over five years through ten years	32,051
Over ten years	0
Fair Value	1,277,378
Amortized Cost	1,258,742
Weighted-Average Yield	2.37%
Weighted-Average Maturity	3.07
Non-agency [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	13
Over five years through ten years	0
Over ten years	0
Fair Value	13
Amortized Cost	13
Weighted-Average Yield	3.99%
Weighted-Average Maturity	2.09
Commercial Collateralized Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	63,366
Over five years through ten years	5,179
Over ten years	0
Fair Value	68,545
Amortized Cost	66,806
Weighted-Average Yield	2.16%
Weighted-Average Maturity	4.52
Corporate Debt Securities [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	23,944
Over five years through ten years	73,398
Over ten years	48,085
Fair Value	145,427
Amortized Cost	$ 157,434
Weighted-Average Yield	1.84%
Weighted-Average Maturity	9.36