GOODWILL AND INTANGIBLE ASSETS - Summary of Other Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 118,670	$ 33,024
Accumulated Amortization	(13,900)	(13,008)
Total	104,770	20,016
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	95,711	10,658
Accumulated Amortization	(6,235)	(5,285)
Total	$ 89,476	$ 5,373
Amortization Period	10 years	10 years
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 17,561	$ 17,561
Accumulated Amortization	(6,215)	(5,815)
Total	11,346	11,746
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	221	221
Accumulated Amortization	(113)	(101)
Total	$ 108	$ 120
Amortization Period	5 years	5 years
Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 5,177	$ 2,652
Accumulated Amortization	(1,337)	(1,301)
Total	$ 3,840	1,351
Favorable lease asset
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets		1,932
Accumulated Amortization		(506)
Total		$ 1,426
Minimum | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Amortization Period	7 years	7 years
Minimum | Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Amortization Period	10 years	10 years
Minimum | Favorable lease asset
Finite-Lived Intangible Assets [Line Items]
Amortization Period		10 months
Maximum | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Amortization Period	15 years	15 years
Maximum | Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Amortization Period	30 years	30 years
Maximum | Favorable lease asset
Finite-Lived Intangible Assets [Line Items]
Amortization Period		15 years