The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Bank deposits belonging to an acquired bank that can be counted on as a stable source of lending funds. These deposits have the following attributes: predictable costs and low sensitivity to interest rates. This intangible asset is usually amortized over its estimated useful life.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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GOODWILL AND OTHER INTANGIBLE ASSETS--Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Goodwill			$ 676,949	$ 0	$ 0
Goodwill	$ 881,033		881,033		204,084	$ 204,084
Intangible Assets, Net (Excluding Goodwill)	53,300		53,300		5,300
Finite-Lived Core Deposits, Gross	40,200		40,200		$ 3,300
Finite-Lived Intangible Assets, Amortization Expense	$ 2,500	$ 300	$ 5,100	$ 1,000
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets amortization method			accelerated basis
Estimated weighted average life (in years)			9 years 1 month 6 days