GOODWILL AND OTHER INTANGIBLE ASSETS (Net Carrying Amount of Goodwill By Segment) (Detail) $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 347,149
Ending balance	370,549
Acquisition of Rembert Pendleton Jackson
Goodwill [Roll Forward]
Acquisitions	22,559
Acquisition of Revere Bank
Goodwill [Roll Forward]
Acquisitions	841
Community Banking
Goodwill [Roll Forward]
Beginning balance	331,173
Ending balance	332,014
Community Banking \| Acquisition of Rembert Pendleton Jackson
Goodwill [Roll Forward]
Acquisitions	0
Community Banking \| Acquisition of Revere Bank
Goodwill [Roll Forward]
Acquisitions	841
Insurance
Goodwill [Roll Forward]
Beginning balance	6,788
Ending balance	6,788
Insurance \| Acquisition of Rembert Pendleton Jackson
Goodwill [Roll Forward]
Acquisitions	0
Insurance \| Acquisition of Revere Bank
Goodwill [Roll Forward]
Acquisitions	0
Investment Management
Goodwill [Roll Forward]
Beginning balance	9,188
Ending balance	31,747
Investment Management \| Acquisition of Rembert Pendleton Jackson
Goodwill [Roll Forward]
Acquisitions	22,559
Investment Management \| Acquisition of Revere Bank
Goodwill [Roll Forward]
Acquisitions	$ 0

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://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

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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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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- Definition

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+ References

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