GOODWILL AND INTANGIBLE ASSETS - Summary of Acquired Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 131,565	$ 80,955
Accumulated Amortization	39,979	22,266
Core deposit premiums
Finite-Lived Intangible Assets [Line Items]
Gross Amount	107,958	57,348
Accumulated Amortization	34,220	19,512
Insurance agent relationships
Finite-Lived Intangible Assets [Line Items]
Gross Amount	22,351	22,351
Accumulated Amortization	5,355	2,561
US Premium Finance trade name
Finite-Lived Intangible Assets [Line Items]
Gross Amount	1,094	1,094
Accumulated Amortization	300	143
Non-compete agreement
Finite-Lived Intangible Assets [Line Items]
Gross Amount	162	162
Accumulated Amortization	$ 104	$ 50