Investment Securities (Amortized Cost And Estimated Fair Value By Contractual Maturity Of Investment Securities Available For Sale) (Details) $ in Thousands	Sep. 30, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	$ 19,933
1 to 5 Years, Amortized Cost	61,491
5 to 10 Years, Amortized Cost	983,131
More Than 10 years, Amortized Cost	2,484,074
No Stated Maturity, Amortized Cost	5,982
Total, Amortized Cost	3,554,611
Within One Year, Fair Value	19,968
1 to 5 Years, Fair Value	62,400
5 to 10 Years, Fair Value	994,497
More Than 10 years, Fair Value	2,514,470
No Stated Maturity, Fair Value	11,818
Total, Fair Value	3,603,153
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	18,770
1 to 5 Years, Amortized Cost	54,988
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	73,758
Within One Year, Fair Value	18,770
1 to 5 Years, Fair Value	55,742
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	74,512
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	999
1 to 5 Years, Amortized Cost	5,929
5 to 10 Years, Amortized Cost	5,800
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	12,728
Within One Year, Fair Value	1,034
1 to 5 Years, Fair Value	6,071
5 to 10 Years, Fair Value	6,038
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	13,143
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	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	0
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	0
Total, Fair Value	0
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	15,175
More Than 10 years, Amortized Cost	166,597
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	181,772
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	15,568
More Than 10 years, Fair Value	169,583
No Stated Maturity, Fair Value	0
Total, Fair Value	185,151
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	334
5 to 10 Years, Amortized Cost	947,156
More Than 10 years, Amortized Cost	1,444,288
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	2,391,778
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	345
5 to 10 Years, Fair Value	957,800
More Than 10 years, Fair Value	1,464,511
No Stated Maturity, Fair Value	0
Total, Fair Value	2,422,656
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	868,723
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	868,723
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	876,109
No Stated Maturity, Fair Value	0
Total, Fair Value	876,109
State And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	164
1 to 5 Years, Amortized Cost	240
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	2,466
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	2,870
Within One Year, Fair Value	164
1 to 5 Years, Fair Value	242
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	2,493
No Stated Maturity, Fair Value	0
Total, Fair Value	2,899
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
No Stated Maturity, Amortized Cost	2,755
Total, Amortized Cost	2,755
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	8,647
Total, Fair Value	8,647
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	3,227
Total, Amortized Cost	20,227
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	15,091
More Than 10 years, Fair Value	1,774
No Stated Maturity, Fair Value	3,171
Total, Fair Value	$ 20,036