Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	$ 2,935,267	$ 2,979,547
Securities Held to Maturity, Gross Unrealized Gains	49,578	5,782
Securities Held to Maturity, Gross Unrealized Losses	5,444	49,473
Securities Held to Maturity, Fair Value	2,979,401	2,935,856
U.S. Treasury And Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	50,000	50,000
Securities Held to Maturity, Gross Unrealized Losses	119	478
Securities Held to Maturity, Fair Value	49,881	49,522
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	653,105	688,201
Securities Held to Maturity, Gross Unrealized Gains	21,047	2,347
Securities Held to Maturity, Gross Unrealized Losses	86	9,503
Securities Held to Maturity, Fair Value	674,066	681,045
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	582,429	640,393
Securities Held to Maturity, Gross Unrealized Gains	9,126	1,461
Securities Held to Maturity, Gross Unrealized Losses	791	6,117
Securities Held to Maturity, Fair Value	590,764	635,737
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	511,138	357,175
Securities Held to Maturity, Gross Unrealized Gains	11,685	376
Securities Held to Maturity, Gross Unrealized Losses	619	10,882
Securities Held to Maturity, Fair Value	522,204	346,669
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	1,138,595	1,243,778
Securities Held to Maturity, Gross Unrealized Gains	7,720	1,598
Securities Held to Maturity, Gross Unrealized Losses	3,829	22,493
Securities Held to Maturity, Fair Value	$ 1,142,486	$ 1,222,883

Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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- Definition

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

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- Definition

Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

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- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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