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, 2018 USD ($)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	$ 21,393
Amortized Cost, 1 to 5 Years	162,734
Amortized Cost, 5 to 10 Years	641,769
Amortized Cost, More Than 10 years	3,260,017
Total Amortized Cost	4,085,913
Fair Value, Within One year	21,398
Fair Value, 1 to 5 Years	161,078
Fair Value, 5 to 10 Years	629,857
Fair Value, More Than 10 years	3,179,299
Total Fair Value	3,991,632
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	19,476
Amortized Cost, 1 to 5 Years	103,960
Amortized Cost, 5 to 10 Years	0
Amortized Cost, More Than 10 years	0
Total Amortized Cost	123,436
Fair Value, Within One year	19,476
Fair Value, 1 to 5 Years	102,601
Fair Value, 5 to 10 Years	0
Fair Value, More Than 10 years	0
Total Fair Value	122,077
U.S. Government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	1,917
Amortized Cost, 1 to 5 Years	6,118
Amortized Cost, 5 to 10 Years	29,986
Amortized Cost, More Than 10 years	0
Total Amortized Cost	38,021
Fair Value, Within One year	1,922
Fair Value, 1 to 5 Years	6,161
Fair Value, 5 to 10 Years	30,299
Fair Value, More Than 10 years	0
Total Fair Value	38,382
Mortgage-backed securities issued by U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	24,076
Amortized Cost, More Than 10 years	75,984
Total Amortized Cost	100,060
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	23,698
Fair Value, More Than 10 years	73,507
Total Fair Value	97,205
Mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	52,656
Amortized Cost, 5 to 10 Years	414,265
Amortized Cost, More Than 10 years	1,993,577
Total Amortized Cost	2,460,498
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	52,316
Fair Value, 5 to 10 Years	404,554
Fair Value, More Than 10 years	1,941,780
Total Fair Value	2,398,650
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	26,950
Amortized Cost, More Than 10 years	1,188,456
Total Amortized Cost	1,215,406
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	26,291
Fair Value, More Than 10 years	1,162,227
Total Fair Value	1,188,518
Commercial mortgage-backed securities issued by U.S. Government sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Within One year	0
Amortized Cost, 1 to 5 Years	0
Amortized Cost, 5 to 10 Years	131,492
Amortized Cost, More Than 10 years	0
Total Amortized Cost	131,492
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	129,865
Fair Value, More Than 10 years	0
Total Fair Value	129,865
State and municipal securities
Debt Securities, Available-for-sale [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
Total Amortized Cost	17,000
Fair Value, Within One year	0
Fair Value, 1 to 5 Years	0
Fair Value, 5 to 10 Years	15,150
Fair Value, More Than 10 years	1,785
Total Fair Value	$ 16,935