Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	$ 3,069,262	$ 2,977,511
Securities Held to Maturity, Gross Unrealized Gains	355	13,110
Securities Held to Maturity, Gross Unrealized Losses	94,162	28,611
Securities Held to Maturity, Fair Value	2,975,455	2,962,010
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	708	289
Securities Held to Maturity, Fair Value	49,292	49,711
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	699,470	723,094
Securities Held to Maturity, Gross Unrealized Gains	355	8,323
Securities Held to Maturity, Gross Unrealized Losses	17,809	4,245
Securities Held to Maturity, Fair Value	682,016	727,172
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	668,320	725,748
Securities Held to Maturity, Gross Unrealized Gains		4,175
Securities Held to Maturity, Gross Unrealized Losses	15,501	2,690
Securities Held to Maturity, Fair Value	652,819	727,233
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	357,428	317,185
Securities Held to Maturity, Gross Unrealized Gains		40
Securities Held to Maturity, Gross Unrealized Losses	17,429	3,915
Securities Held to Maturity, Fair Value	339,999	313,310
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Amortized Cost	1,294,044	1,161,484
Securities Held to Maturity, Gross Unrealized Gains		572
Securities Held to Maturity, Gross Unrealized Losses	42,715	17,472
Securities Held to Maturity, Fair Value	$ 1,251,329	$ 1,144,584

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

+ Details

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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=82897076&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=82897076&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=82897076&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

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