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
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
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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.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e961-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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Goodwill and Other Intangible Assets - Schedule of Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands		3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Goodwill
Balance at beginning of the period		$ 1,188,902		$ 726,856
Goodwill acquired during the year (preliminary allocation)				462,046
Goodwill acquired during the year (preliminary allocation) and adjustments		47,267
Balance at end of the period	$ 1,236,169	1,236,169	$ 1,236,169
Operating Segments \| IBERIABANK
Goodwill
Balance at beginning of the period		1,160,559		698,513
Goodwill acquired during the year (preliminary allocation)				462,046
Goodwill acquired during the year (preliminary allocation) and adjustments		43,887
Balance at end of the period	1,204,446	1,204,446	1,204,446
Operating Segments \| IMC
Goodwill
Balance at beginning of the period		23,178		23,178
Goodwill acquired during the year (preliminary allocation)				0
Goodwill acquired during the year (preliminary allocation) and adjustments		0
Balance at end of the period	23,178	23,178	23,178
Operating Segments \| LTC
Goodwill
Balance at beginning of the period		5,165		5,165
Goodwill acquired during the year (preliminary allocation)				$ 0
Goodwill acquired during the year (preliminary allocation) and adjustments		3,380
Balance at end of the period	8,545	$ 8,545	8,545
Gibraltar Private Bank & Trust Company
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments	$ 42,500
Solomon Parks Title & Escrow
Goodwill
Goodwill acquired during the year (preliminary allocation) and adjustments			$ 3,400