Securities (Amortized Cost and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	$ 3,008,951	$ 2,949,057
Securities Available for Sale, Gross Unrealized Gains	3,763	7,230
Securities Available for Sale, Gross Unrealized Losses	97,066	45,418
Securities Available for Sale, Fair Value	2,915,648	2,910,869
U.S. Treasury And Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	97,431	99,535
Securities Available for Sale, Gross Unrealized Losses	3,547	2,263
Securities Available for Sale, Fair Value	93,884	97,272
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	245,164	245,997
Securities Available for Sale, Gross Unrealized Gains	211	1,135
Securities Available for Sale, Gross Unrealized Losses	8,084	3,346
Securities Available for Sale, Fair Value	237,291	243,786
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	1,787,382	1,729,989
Securities Available for Sale, Gross Unrealized Gains	3,552	5,611
Securities Available for Sale, Gross Unrealized Losses	47,391	20,387
Securities Available for Sale, Fair Value	1,743,543	1,715,213
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	715,360	704,518
Securities Available for Sale, Gross Unrealized Gains		480
Securities Available for Sale, Gross Unrealized Losses	35,088	17,863
Securities Available for Sale, Fair Value	680,272	687,135
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	158,114	165,518
Securities Available for Sale, Gross Unrealized Gains		4
Securities Available for Sale, Gross Unrealized Losses	2,956	1,559
Securities Available for Sale, Fair Value	155,158	163,963
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	5,500	3,500
Securities Available for Sale, Fair Value	$ 5,500	$ 3,500

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: 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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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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