Investment Securities (Summary Of Available For Sale Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 3,831,934	$ 3,768,618
Gross Unrealized Gains	5,065	11,114
Gross Unrealized Losses	(54,057)	(61,537)
Fair Value	3,782,942	3,718,195
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	83,441	108,221
Gross Unrealized Gains	0	225
Gross Unrealized Losses	(550)	(644)
Fair Value	82,891	107,802
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,089	12,727
Gross Unrealized Gains	342	266
Gross Unrealized Losses	0	0
Fair Value	12,431	12,993
Mortgage-Backed Securities Issued By U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	166,794	174,440
Gross Unrealized Gains	787	1,116
Gross Unrealized Losses	(1,302)	(1,354)
Fair Value	166,279	174,202
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,837,359	2,543,495
Gross Unrealized Gains	3,779	5,416
Gross Unrealized Losses	(38,594)	(42,571)
Fair Value	2,802,544	2,506,340
Collateralized Mortgage Obligations Issued By U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	710,188	905,789
Gross Unrealized Gains	12	1,214
Gross Unrealized Losses	(13,308)	(16,561)
Fair Value	696,892	890,442
State And Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,800	2,780
Gross Unrealized Gains	1	14
Gross Unrealized Losses	0	0
Fair Value	1,801	2,794
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		919
Gross Unrealized Gains		2,863
Gross Unrealized Losses		0
Fair Value		3,782
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,263	20,247
Gross Unrealized Gains	144	0
Gross Unrealized Losses	(303)	(407)
Fair Value	$ 20,104	$ 19,840

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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