Investment Securities (Details 4) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2011
Securities Available for Sale
One year or less	$ 309,130
Over one year through five years	2,675,146
Over five years through ten years	319,352
Over ten years	190,892
Fair Value	3,494,520
Weighted Average Yield, one year or less	1.35%
Weighted Average Yield, over one year through five years	2.92%
Weighted Average Yield, over five years through ten years	3.34%
Weighted Average Yield, over ten years	4.55%
Weighted Average Yield, Total	2.92%
Amortized Cost	3,415,011
Weighted-Average Yield	2.92%
Weighted-Average Maturity	3.7
Securities Held to Maturity
One year or less	27,770
Over one year through five years	14,507
Over five years through ten years	3,780
Over ten years	34,800
Fair Value	80,857
Weighted Average Yield, one year or less	3.79%
Weighted Average Yield, over one year through five years	3.79%
Weighted Average Yield, over five years through ten years	3.79%
Weighted Average Yield, over ten years	7.29%
Weighted Average Yield, Total	5.30%
Amortized Cost	80,857
Weighted Average Yield	5.30%
Weighted-Average Maturity	7.4
U.S. government agency debentures [Member]
Securities Available for Sale
One year or less	259,805
Over one year through five years	111,439
Over five years through ten years	0
Over ten years	0
Fair Value	371,244
Amortized Cost	370,649
Weighted-Average Yield	0.74%
Weighted-Average Maturity	0.7
U.S. government agency debentures [Member]
Securities Held to Maturity
One year or less	0
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	0
Amortized Cost	0
U.S. States and political subdivisions [Member]
Securities Held to Maturity
One year or less	27,770
Over one year through five years	14,507
Over five years through ten years	3,780
Over ten years	34,800
Fair Value	80,857
Amortized Cost	80,857
Weighted Average Yield	5.30%
Weighted-Average Maturity	7.4
U.S. States and political subdivisions [Member]
Securities Available for Sale
One year or less	10,313
Over one year through five years	21,351
Over five years through ten years	137,952
Over ten years	140,169
Fair Value	309,785
Amortized Cost	299,238
Weighted-Average Yield	5.69%
Weighted-Average Maturity	9.1
Residential Mortgage Backed Securities Issued By US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	4,067
Over one year through five years	1,479,708
Over five years through ten years	105,196
Over ten years	0
Fair Value	1,588,971
Amortized Cost	1,528,537
Weighted-Average Yield	3.45%
Weighted-Average Maturity	3.3
Residential Mortgage Backed Securities Issued By US Government Sponsored Enterprises [Member]
Securities Held to Maturity
One year or less	0
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	0
Amortized Cost	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities Available for Sale
One year or less	34,945
Over one year through five years	1,045,005
Over five years through ten years	0
Over ten years	0
Fair Value	1,079,950
Amortized Cost	1,061,393
Weighted-Average Yield	2.43%
Weighted-Average Maturity	2.8
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities Held to Maturity
One year or less	0
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	0
Amortized Cost	0
Non-agency [Member]
Securities Available for Sale
One year or less	0
Over one year through five years	17,643
Over five years through ten years	76,204
Over ten years	0
Fair Value	93,847
Amortized Cost	93,733
Weighted-Average Yield	0.62%
Weighted-Average Maturity	5.9
Non-agency [Member]
Securities Held to Maturity
One year or less	0
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	0
Amortized Cost	0
Corporate debt securities [Member]
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	50,723
Fair Value	50,723
Amortized Cost	61,461
Weighted-Average Yield	0.91%
Weighted-Average Maturity	16.3
Corporate debt securities [Member]
Securities Held to Maturity
One year or less	0
Over one year through five years	0
Over five years through ten years	0
Over ten years	0
Fair Value	0
Amortized Cost	$ 0