Securities (Amortized Cost and Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	$ 1,568,009	$ 2,979,547
Securities Held to Maturity, Gross Unrealized Gains	44,103	5,782
Securities Held to Maturity, Gross Unrealized Losses	1,108	49,473
Securities Held to Maturity, Fair Value	1,611,004	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 Gains	3
Securities Held to Maturity, Gross Unrealized Losses		478
Securities Held to Maturity, Fair Value	50,003	49,522
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	641,019	688,201
Securities Held to Maturity, Gross Unrealized Gains	27,146	2,347
Securities Held to Maturity, Gross Unrealized Losses	69	9,503
Securities Held to Maturity, Fair Value	668,096	681,045
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	29,687	640,393
Securities Held to Maturity, Gross Unrealized Gains	883	1,461
Securities Held to Maturity, Gross Unrealized Losses		6,117
Securities Held to Maturity, Fair Value	30,570	635,737
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	539,371	357,175
Securities Held to Maturity, Gross Unrealized Gains	12,474	376
Securities Held to Maturity, Gross Unrealized Losses	581	10,882
Securities Held to Maturity, Fair Value	551,264	346,669
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Gross Amortized Cost	307,932	1,243,778
Securities Held to Maturity, Gross Unrealized Gains	3,597	1,598
Securities Held to Maturity, Gross Unrealized Losses	458	22,493
Securities Held to Maturity, Fair Value	$ 311,071	$ 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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