Investment Securities Available for Sale (Amortized Cost And Estimated Fair Value By Contractual Maturity Of Investment Securities Available For Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost
Within One year, Amortized Cost	$ 21,439
1 to 5 Years, Amortized Cost	111,715
5 to 10 Years, Amortized Cost	707,400
More Than 10 years, Amortized Cost	3,226,047
Amortized Cost	4,066,601	$ 4,038,239
Fair Value
Within One Year, Fair Value	21,446
1 to 5 Years, Fair Value	109,615
5 to 10 Years, Fair Value	687,815
More Than 10 years, Fair Value	3,111,086
Total, Fair Value	3,929,962	3,987,069
U.S. Treasury securities
Amortized Cost
Within One year, Amortized Cost	18,993
1 to 5 Years, Amortized Cost	103,807
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
Amortized Cost	122,800	83,608
Fair Value
Within One Year, Fair Value	18,993
1 to 5 Years, Fair Value	101,640
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
Total, Fair Value	120,633	82,674
U.S. Government agency securities
Amortized Cost
Within One year, Amortized Cost	2,330
1 to 5 Years, Amortized Cost	6,437
5 to 10 Years, Amortized Cost	31,986
More Than 10 years, Amortized Cost	0
Amortized Cost	40,753	10,771
Fair Value
Within One Year, Fair Value	2,337
1 to 5 Years, Fair Value	6,455
5 to 10 Years, Fair Value	32,142
More Than 10 years, Fair Value	0
Total, Fair Value	40,934	10,862
Mortgage-backed securities issued by U.S. Government agencies
Amortized Cost
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	27,725
More Than 10 years, Amortized Cost	83,681
Amortized Cost	111,406	121,283
Fair Value
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	27,266
More Than 10 years, Fair Value	80,678
Total, Fair Value	107,944	120,440
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Amortized Cost
Within One year, Amortized Cost	1
1 to 5 Years, Amortized Cost	1,471
5 to 10 Years, Amortized Cost	615,334
More Than 10 years, Amortized Cost	1,997,862
Amortized Cost	2,614,668	2,666,818
Fair Value
Within One Year, Fair Value	1
1 to 5 Years, Fair Value	1,520
5 to 10 Years, Fair Value	596,366
More Than 10 years, Fair Value	1,928,958
Total, Fair Value	2,526,845	2,640,523
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Amortized Cost
Within One year, Amortized Cost	0
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	17,355
More Than 10 years, Amortized Cost	1,142,504
Amortized Cost	1,159,859
Fair Value
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	16,855
More Than 10 years, Fair Value	1,099,593
Total, Fair Value	1,116,448
State and municipal securities
Amortized Cost
Within One year, Amortized Cost	115
1 to 5 Years, Amortized Cost	0
5 to 10 Years, Amortized Cost	0
More Than 10 years, Amortized Cost	0
Amortized Cost	115	180
Fair Value
Within One Year, Fair Value	115
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	0
More Than 10 years, Fair Value	0
Total, Fair Value	115	180
Corporate debt and other debt securities
Amortized Cost
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
Amortized Cost	17,000	20,320
Fair Value
Within One Year, Fair Value	0
1 to 5 Years, Fair Value	0
5 to 10 Years, Fair Value	15,186
More Than 10 years, Fair Value	1,857
Total, Fair Value	$ 17,043	$ 20,391

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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