Goodwill and Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Changes In Carrying Amount of Goodwill
Beginning balance	$ 470,534	$ 445,871
Addition to goodwill	140,512	20,633
Adjustment to previously recorded goodwill		4,030
Ending balance	611,046	470,534
Community Banks
Changes In Carrying Amount of Goodwill
Beginning balance	467,767	443,104
Addition to goodwill	140,512	20,633
Adjustment to previously recorded goodwill		4,030
Ending balance	608,279	467,767
Insurance
Changes In Carrying Amount of Goodwill
Beginning balance	2,767	2,767
Addition to goodwill	0	0
Adjustment to previously recorded goodwill		0
Ending balance	$ 2,767	$ 2,767

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of transfers into (out of) an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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