Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	$ 2,977,511	$ 2,500,220
Securities Held to Maturity, Gross Unrealized Gains	13,110	7,896
Securities Held to Maturity, Gross Unrealized Losses	28,611	37,999
Securities Held to Maturity, Fair Value	2,962,010	2,470,117
U.S. Treasury And Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	50,000	50,000
Securities Held to Maturity, Gross Unrealized Losses	289	44
Securities Held to Maturity, Fair Value	49,711	49,956
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	723,094	648,093
Securities Held to Maturity, Gross Unrealized Gains	8,323	2,147
Securities Held to Maturity, Gross Unrealized Losses	4,245	20,175
Securities Held to Maturity, Fair Value	727,172	630,065
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	725,748	862,162
Securities Held to Maturity, Gross Unrealized Gains	4,175	4,329
Securities Held to Maturity, Gross Unrealized Losses	2,690	3,068
Securities Held to Maturity, Fair Value	727,233	863,423
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	317,185	75,739
Securities Held to Maturity, Gross Unrealized Gains	40
Securities Held to Maturity, Gross Unrealized Losses	3,915	4,038
Securities Held to Maturity, Fair Value	313,310	71,701
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	1,161,484	864,226
Securities Held to Maturity, Gross Unrealized Gains	572	1,420
Securities Held to Maturity, Gross Unrealized Losses	17,472	10,674
Securities Held to Maturity, Fair Value	$ 1,144,584	$ 854,972

Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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- Definition

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

+ References

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- Definition

Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

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- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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