Securities (Securities Available for Sale) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	$ 19,761	$ 0
Securities available-for-sale, amortized cost	2,683,654		$ 2,763,321
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	4,208		8,480
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	63,817		34,050
Available-for-sale Securities, Debt Securities	2,624,045		2,737,751
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available-for-sale, amortized cost	1,693,149		1,752,236
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	698		1,815
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	48,629		27,326
Available-for-sale Securities, Debt Securities	1,645,218		1,726,725
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available-for-sale, amortized cost	588,218		593,940
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	3,467		6,023
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	8,937		3,959
Available-for-sale Securities, Debt Securities	582,748		596,004
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available-for-sale, amortized cost	402,036		416,894
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	43		642
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	6,247		2,762
Available-for-sale Securities, Debt Securities	395,832		414,774
US Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available-for-sale, amortized cost	251		251
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	0		0
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	4		3
Available-for-sale Securities, Debt Securities	$ 247		$ 248

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

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

+ References

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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-Subparagraph (b)
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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 9
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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