Securities (Securities Available for Sale with Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Losses less than 12 months, Fair Value	$ 1,154,658	$ 842,011
Available for sale, Losses less than 12 months, Gross Unrealized Losses	27,244	6,319
Available for sale, Losses 12 months or longer, Fair Value	1,503,947	1,569,320
Available for sale, Losses 12 months or longer, Gross Unrealized Losses	69,822	39,099
Available for sale, Total, Fair Value	2,658,605	2,411,331
Available for sale, Total, Gross Unrealized Losses	97,066	45,418
U.S. Treasury And Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Losses less than 12 months, Fair Value	43,521	45,616
Available for sale, Losses less than 12 months, Gross Unrealized Losses	1,214	42
Available for sale, Losses 12 months or longer, Fair Value	50,362	51,157
Available for sale, Losses 12 months or longer, Gross Unrealized Losses	2,333	2,221
Available for sale, Total, Fair Value	93,883	96,773
Available for sale, Total, Gross Unrealized Losses	3,547	2,263
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Losses less than 12 months, Fair Value	54,330	2,768
Available for sale, Losses less than 12 months, Gross Unrealized Losses	948	11
Available for sale, Losses 12 months or longer, Fair Value	169,119	173,530
Available for sale, Losses 12 months or longer, Gross Unrealized Losses	7,136	3,335
Available for sale, Total, Fair Value	223,449	176,298
Available for sale, Total, Gross Unrealized Losses	8,084	3,346
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Losses less than 12 months, Fair Value	654,990	461,835
Available for sale, Losses less than 12 months, Gross Unrealized Losses	14,667	4,195
Available for sale, Losses 12 months or longer, Fair Value	850,853	898,099
Available for sale, Losses 12 months or longer, Gross Unrealized Losses	32,724	16,192
Available for sale, Total, Fair Value	1,505,843	1,359,934
Available for sale, Total, Gross Unrealized Losses	47,391	20,387
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Losses less than 12 months, Fair Value	279,631	203,618
Available for sale, Losses less than 12 months, Gross Unrealized Losses	8,091	995
Available for sale, Losses 12 months or longer, Fair Value	400,641	411,046
Available for sale, Losses 12 months or longer, Gross Unrealized Losses	26,997	16,868
Available for sale, Total, Fair Value	680,272	614,664
Available for sale, Total, Gross Unrealized Losses	35,088	17,863
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, Losses less than 12 months, Fair Value	122,186	128,174
Available for sale, Losses less than 12 months, Gross Unrealized Losses	2,324	1,076
Available for sale, Losses 12 months or longer, Fair Value	32,972	35,488
Available for sale, Losses 12 months or longer, Gross Unrealized Losses	632	483
Available for sale, Total, Fair Value	155,158	163,662
Available for sale, Total, Gross Unrealized Losses	$ 2,956	$ 1,559

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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