Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 8,602,599	$ 8,715,456
Debt Securities, Available-for-sale, Fair Value		8,538,041	8,725,442
U.S. Government And Federal Agency Obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		914,486	917,494
Debt Securities, Available-for-sale, Fair Value		$ 907,652	917,147
Weighted Average Yield	[1]	1.63%
U.S. Government And Federal Agency Obligations [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 23,577
Debt Securities, Available-for-sale, Fair Value		$ 23,518
Weighted Average Yield	[1]	(0.04%)
U.S. Government And Federal Agency Obligations [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 434,973
Debt Securities, Available-for-sale, Fair Value		$ 435,690
Weighted Average Yield	[1]	1.90%
U.S. Government And Federal Agency Obligations [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 386,708
Debt Securities, Available-for-sale, Fair Value		$ 381,419
Weighted Average Yield	[1]	1.61%
U.S. Government And Federal Agency Obligations [Member] | Maturity After 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 69,228
Debt Securities, Available-for-sale, Fair Value		$ 67,025
Weighted Average Yield	[1]	0.64%
US Government-sponsored Enterprise Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 199,470	408,266
Debt Securities, Available-for-sale, Fair Value		$ 195,778	406,363
Weighted Average Yield		2.32%
US Government-sponsored Enterprise Debt Securities [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 24,991
Debt Securities, Available-for-sale, Fair Value		$ 24,743
Weighted Average Yield		1.53%
US Government-sponsored Enterprise Debt Securities [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 96,601
Debt Securities, Available-for-sale, Fair Value		$ 95,619
Weighted Average Yield		2.03%
US Government-sponsored Enterprise Debt Securities [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 34,985
Debt Securities, Available-for-sale, Fair Value		$ 34,460
Weighted Average Yield		2.71%
US Government-sponsored Enterprise Debt Securities [Member] | Maturity After 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 42,893
Debt Securities, Available-for-sale, Fair Value		$ 40,956
Weighted Average Yield		3.10%
State and municipal obligations [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 1,322,785	1,592,707
Debt Securities, Available-for-sale, Fair Value		$ 1,328,039	1,611,366
Weighted Average Yield		2.50%
State and municipal obligations [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 98,429
Debt Securities, Available-for-sale, Fair Value		$ 98,675
Weighted Average Yield		2.45%
State and municipal obligations [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 656,762
Debt Securities, Available-for-sale, Fair Value		$ 659,525
Weighted Average Yield		2.37%
State and municipal obligations [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 493,994
Debt Securities, Available-for-sale, Fair Value		$ 496,997
Weighted Average Yield		2.58%
State and municipal obligations [Member] | Maturity After 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 73,600
Debt Securities, Available-for-sale, Fair Value		$ 72,842
Weighted Average Yield		3.22%
Agency mortgage-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 3,253,433	3,046,701
Debt Securities, Available-for-sale, Fair Value		$ 3,214,985	3,040,913
Weighted Average Yield		2.85%
Non-agency mortgage-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 1,053,854	903,920
Debt Securities, Available-for-sale, Fair Value		$ 1,047,716	905,793
Weighted Average Yield		2.85%
Asset-backed Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 1,518,976	1,495,380
Debt Securities, Available-for-sale, Fair Value		$ 1,511,614	1,492,800
Weighted Average Yield		2.62%
Total mortgage and asset-backed securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 5,826,263	5,446,001
Debt Securities, Available-for-sale, Fair Value		$ 5,774,315	5,439,506
Weighted Average Yield		2.79%
Other Debt Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		$ 339,595	350,988
Debt Securities, Available-for-sale, Fair Value		332,257	$ 351,060
Other Debt Securities [Member] | Maturity Within 1 Year [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		16,500
Debt Securities, Available-for-sale, Fair Value		16,418
Other Debt Securities [Member] | Maturity After 1 But Within 5 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		249,870
Debt Securities, Available-for-sale, Fair Value		245,319
Other Debt Securities [Member] | Maturity After 5 But Within 10 Years [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		73,225
Debt Securities, Available-for-sale, Fair Value		$ 70,520

[1] Rate does not reflect inflation adjustment on inflation-protected securities