Securities (Amortized Cost and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	$ 3,091,620	$ 2,949,057
Securities Available for Sale, Gross Unrealized Gains	2,927	7,230
Securities Available for Sale, Gross Unrealized Losses	112,874	45,418
Securities Available for Sale, Fair Value	2,981,673	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	95,469	99,535
Securities Available for Sale, Gross Unrealized Losses	4,484	2,263
Securities Available for Sale, Fair Value	90,985	97,272
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	244,365	245,997
Securities Available for Sale, Gross Unrealized Gains	165	1,135
Securities Available for Sale, Gross Unrealized Losses	8,520	3,346
Securities Available for Sale, Fair Value	236,010	243,786
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	1,826,589	1,729,989
Securities Available for Sale, Gross Unrealized Gains	2,609	5,611
Securities Available for Sale, Gross Unrealized Losses	54,327	20,387
Securities Available for Sale, Fair Value	1,774,871	1,715,213
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	770,769	704,518
Securities Available for Sale, Gross Unrealized Gains	153	480
Securities Available for Sale, Gross Unrealized Losses	41,390	17,863
Securities Available for Sale, Fair Value	729,532	687,135
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	150,928	165,518
Securities Available for Sale, Gross Unrealized Gains		4
Securities Available for Sale, Gross Unrealized Losses	4,153	1,559
Securities Available for Sale, Fair Value	146,775	163,963
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	3,500	3,500
Securities Available for Sale, Fair Value	$ 3,500	$ 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
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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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+ 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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