Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	$ 2,855,062	$ 2,979,547
Securities Held to Maturity, Gross Unrealized Gains	67,858	5,782
Securities Held to Maturity, Gross Unrealized Losses	2,564	49,473
Securities Held to Maturity, Fair Value	2,920,356	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	46	478
Securities Held to Maturity, Fair Value	49,954	49,522
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	647,500	688,201
Securities Held to Maturity, Gross Unrealized Gains	28,613	2,347
Securities Held to Maturity, Gross Unrealized Losses	95	9,503
Securities Held to Maturity, Fair Value	676,018	681,045
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	549,929	640,393
Securities Held to Maturity, Gross Unrealized Gains	9,226	1,461
Securities Held to Maturity, Gross Unrealized Losses	355	6,117
Securities Held to Maturity, Fair Value	558,800	635,737
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	539,877	357,175
Securities Held to Maturity, Gross Unrealized Gains	20,099	376
Securities Held to Maturity, Gross Unrealized Losses	10	10,882
Securities Held to Maturity, Fair Value	559,966	346,669
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	1,067,756	1,243,778
Securities Held to Maturity, Gross Unrealized Gains	9,920	1,598
Securities Held to Maturity, Gross Unrealized Losses	2,058	22,493
Securities Held to Maturity, Fair Value	$ 1,075,618	$ 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=118939692&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=118939692&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=118939692&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.

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