Investment Securities (Amortized Cost And Estimated Fair Value By Contractual Maturity Of Investment Securities Available For Sale) (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	$ 19,948
1 to 5 Years, Amortized Cost	72,756
5 to 10 Years, Amortized Cost	612,552
More Than 10 years, Amortized Cost	3,156,363
No Stated Maturity, Amortized Cost	3,279
Total, Amortized Cost	3,864,898
Within One Year, Fair Value	19,953
1 to 5 Years, Fair Value	72,594
5 to 10 Years, Fair Value	607,755
More Than 10 years, Fair Value	3,123,614
No Stated Maturity, Fair Value	3,142
Total, Fair Value	3,827,058
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	18,791
1 to 5 Years, Amortized Cost	64,702
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	83,493
Within One Year, Fair Value	18,791
1 to 5 Years, Fair Value	64,342
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	83,133
U.S. Government agency securities
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	1,000
1 to 5 Years, Amortized Cost	5,612
5 to 10 Years, Amortized Cost	5,476
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	12,088
Within One Year, Fair Value	1,004
1 to 5 Years, Fair Value	5,682
5 to 10 Years, Fair Value	5,625
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	12,311
Mortgage-backed securities issued by U.S. Government agencies
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	34,868
More Than 10 years, Amortized Cost	97,842
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	132,710
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	35,007
More Than 10 years, Fair Value	97,218
No Stated Maturity, Fair Value	0
Total, Fair Value	132,225
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	47
1 to 5 Years, Amortized Cost	2,262
5 to 10 Years, Amortized Cost	535,035
More Than 10 years, Amortized Cost	2,343,890
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	2,881,234
Within One Year, Fair Value	48
1 to 5 Years, Fair Value	2,390
5 to 10 Years, Fair Value	529,968
More Than 10 years, Fair Value	2,323,999
No Stated Maturity, Fair Value	0
Total, Fair Value	2,856,405
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
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	22,173
More Than 10 years, Amortized Cost	712,631
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	734,804
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	21,950
More Than 10 years, Fair Value	700,470
No Stated Maturity, Fair Value	0
Total, Fair Value	722,420
State and municipal securities
Schedule of Available-for-sale Securities [Line Items]
Within One year, Amortized Cost	110
1 to 5 Years, Amortized Cost	180
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
No Stated Maturity, Amortized Cost	0
Total, Amortized Cost	290
Within One Year, Fair Value	110
1 to 5 Years, Fair Value	180
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
No Stated Maturity, Fair Value	0
Total, Fair Value	290
Corporate debt and other securities
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	3,279
Total, Amortized Cost	20,279
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	15,205
More Than 10 years, Fair Value	1,927
No Stated Maturity, Fair Value	3,142
Total, Fair Value	$ 20,274