Investment Securities Available for Sale (Amortized Cost And Estimated Fair Value By Contractual Maturity Of Investment Securities Available For Sale) (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	$ 19,698
Amortized Cost, 1 to 5 Years	96,041
Amortized Cost, 5 to 10 Years	659,705
Amortized Cost, More Than 10 years	2,989,008
Amortized Cost, Amortized Cost, No Stated Maturity	4,166
Total Amortized Cost	3,768,618
Fair Value, Within One year	19,724
Fair Value, 1 to 5 Years	95,714
Fair Value, 5 to 10 Years	659,905
Fair Value, More Than 10 years	2,935,978
Fair Value, No Stated Maturity	6,874
Total Fair Value	3,718,195
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	18,435
Amortized Cost, 1 to 5 Years	89,786
Amortized Cost, 5 to 10 Years	0
Amortized Cost, More Than 10 years	0
Amortized Cost, Amortized Cost, No Stated Maturity	0
Total Amortized Cost	108,221
Fair Value, Within One year	18,435
Fair Value, 1 to 5 Years	89,367
Fair Value, 5 to 10 Years	0
Fair Value, More Than 10 years	0
Fair Value, No Stated Maturity	0
Total Fair Value	107,802
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	999
Amortized Cost, 1 to 5 Years	5,929
Amortized Cost, 5 to 10 Years	5,799
Amortized Cost, More Than 10 years	0
Amortized Cost, Amortized Cost, No Stated Maturity	0
Total Amortized Cost	12,727
Fair Value, Within One year	1,021
Fair Value, 1 to 5 Years	6,019
Fair Value, 5 to 10 Years	5,953
Fair Value, More Than 10 years	0
Fair Value, No Stated Maturity	0
Total Fair Value	12,993
Mortgage-Backed Securities Issued By U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	14,345
Amortized Cost, More Than 10 years	160,095
Amortized Cost, Amortized Cost, No Stated Maturity	0
Total Amortized Cost	174,440
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	14,784
Fair Value, More Than 10 years	159,418
Fair Value, No Stated Maturity	0
Total Fair Value	174,202
Mortgage-Backed Securities Issued By U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	154
Amortized Cost, 1 to 5 Years	86
Amortized Cost, 5 to 10 Years	624,561
Amortized Cost, More Than 10 years	1,918,694
Amortized Cost, Amortized Cost, No Stated Maturity	0
Total Amortized Cost	2,543,495
Fair Value, Within One year	158
Fair Value, 1 to 5 Years	88
Fair Value, 5 to 10 Years	624,216
Fair Value, More Than 10 years	1,881,878
Fair Value, No Stated Maturity	0
Total Fair Value	2,506,340
Collateralized Mortgage-Backed Securities Issued By U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	0
Amortized Cost, More Than 10 years	905,789
Amortized Cost, Amortized Cost, No Stated Maturity	0
Total Amortized Cost	905,789
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	0
Fair Value, More Than 10 years	890,442
Fair Value, No Stated Maturity	0
Total Fair Value	890,442
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	110
Amortized Cost, 1 to 5 Years	240
Amortized Cost, 5 to 10 Years	0
Amortized Cost, More Than 10 years	2,430
Amortized Cost, Amortized Cost, No Stated Maturity	0
Total Amortized Cost	2,780
Fair Value, Within One year	110
Fair Value, 1 to 5 Years	240
Fair Value, 5 to 10 Years	0
Fair Value, More Than 10 years	2,444
Fair Value, No Stated Maturity	0
Total Fair Value	2,794
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	0
Amortized Cost, More Than 10 years	0
Amortized Cost, Amortized Cost, No Stated Maturity	919
Total Amortized Cost	919
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	0
Fair Value, More Than 10 years	0
Fair Value, No Stated Maturity	3,782
Total Fair Value	3,782
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	15,000
Amortized Cost, More Than 10 years	2,000
Amortized Cost, Amortized Cost, No Stated Maturity	3,247
Total Amortized Cost	20,247
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	14,952
Fair Value, More Than 10 years	1,796
Fair Value, No Stated Maturity	3,092
Total Fair Value	$ 19,840