Investment Securities (Amortized Cost And Estimated Fair Value By Contractual Maturity Of Investment Securities Available For Sale) (Details) $ in Thousands	Mar. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	$ 99,533
1 to 5 Years, Amortized Cost	78,486
5 to 10 Years, Amortized Cost	1,372,713
More Than 10 years, Amortized Cost	1,985,965
No Stated Maturity, Amortized Cost	6,422
Total, Amortized Cost	3,543,119
Within One Year, Fair Value	99,703
1 to 5 Years, Fair Value	79,443
5 to 10 Years, Fair Value	1,380,966
More Than 10 years, Fair Value	2,010,795
No Stated Maturity, Fair Value	11,337
Total, Fair Value	3,582,244
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	18,256
1 to 5 Years, Amortized Cost	24,891
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	43,147
Within One Year, Fair Value	18,256
1 to 5 Years, Fair Value	25,450
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	43,706
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	6,614
5 to 10 Years, Amortized Cost	6,402
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	13,016
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	6,849
5 to 10 Years, Fair Value	6,701
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	13,550
Securities Issued By U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	80,240
1 to 5 Years, Amortized Cost	46,065
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	126,305
Within One Year, Fair Value	80,398
1 to 5 Years, Fair Value	46,204
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	126,602
Mortgage-Backed Securities Issued By U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	17,447
More Than 10 years, Amortized Cost	173,939
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	191,386
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	17,810
More Than 10 years, Fair Value	176,086
No Stated Maturity, Fair Value	0
Total, Fair Value	193,896
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	566
5 to 10 Years, Amortized Cost	1,333,864
More Than 10 years, Amortized Cost	1,264,688
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	2,599,118
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	588
5 to 10 Years, Fair Value	1,341,168
More Than 10 years, Fair Value	1,280,378
No Stated Maturity, Fair Value	0
Total, Fair Value	2,622,134
Collateralized Mortgage-Backed Securities Issued By U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	542,761
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	542,761
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	550,055
No Stated Maturity, Fair Value	0
Total, Fair Value	550,055
State And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	1,037
1 to 5 Years, Amortized Cost	350
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	2,577
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	3,964
Within One Year, Fair Value	1,049
1 to 5 Years, Fair Value	352
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	2,638
No Stated Maturity, Fair Value	0
Total, Fair Value	4,039
Securities With No Stated Maturity (Equity Securities) [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	3,228
Total, Amortized Cost	3,228
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	8,204
Total, Fair Value	8,204
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	15,000
More Than 10 years, Amortized Cost	2,000
No Stated Maturity, Amortized Cost	3,194
Total, Amortized Cost	20,194
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	15,287
More Than 10 years, Fair Value	1,638
No Stated Maturity, Fair Value	3,133
Total, Fair Value	$ 20,058