Securities (Securities Held to Maturity with Unrealized Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Losses less than 12 months, Fair Value	$ 51,582	$ 401,593
Securities Held to Maturity, Losses less than 12 months, Gross Unrealized Losses	105	2,660
Securities Held to Maturity, Losses 12 months or longer, Fair Value	434,583	1,720,624
Securities Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	2,459	46,813
Securities Held to Maturity, Total, Fair Value	486,165	2,122,217
Securities Held to Maturity, Total, Gross Unrealized Losses	2,564	49,473
U.S. Treasury And Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Losses 12 months or longer, Fair Value	49,954	49,521
Securities Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	46	478
Securities Held to Maturity, Total, Fair Value	49,954	49,521
Securities Held to Maturity, Total, Gross Unrealized Losses	46	478
Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Losses less than 12 months, Fair Value	3,820	233,469
Securities Held to Maturity, Losses less than 12 months, Gross Unrealized Losses	30	2,256
Securities Held to Maturity, Losses 12 months or longer, Fair Value	6,431	233,280
Securities Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	65	7,247
Securities Held to Maturity, Total, Fair Value	10,251	466,749
Securities Held to Maturity, Total, Gross Unrealized Losses	95	9,503
Residential Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Losses less than 12 months, Fair Value		90,730
Securities Held to Maturity, Losses less than 12 months, Gross Unrealized Losses		123
Securities Held to Maturity, Losses 12 months or longer, Fair Value	122,687	235,251
Securities Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	355	5,994
Securities Held to Maturity, Total, Fair Value	122,687	325,981
Securities Held to Maturity, Total, Gross Unrealized Losses	355	6,117
Commercial Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Losses less than 12 months, Fair Value	29,101
Securities Held to Maturity, Losses less than 12 months, Gross Unrealized Losses	10
Securities Held to Maturity, Losses 12 months or longer, Fair Value		305,419
Securities Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses		10,882
Securities Held to Maturity, Total, Fair Value	29,101	305,419
Securities Held to Maturity, Total, Gross Unrealized Losses	10	10,882
Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities Held to Maturity, Losses less than 12 months, Fair Value	18,661	77,394
Securities Held to Maturity, Losses less than 12 months, Gross Unrealized Losses	65	281
Securities Held to Maturity, Losses 12 months or longer, Fair Value	255,511	897,153
Securities Held to Maturity, Losses 12 months or longer, Gross Unrealized Losses	1,993	22,212
Securities Held to Maturity, Total, Fair Value	274,172	974,547
Securities Held to Maturity, Total, Gross Unrealized Losses	$ 2,058	$ 22,493

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section 50
-Paragraph 6
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-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

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