GOODWILL AND INTANGIBLE ASSETS - Summary of Other Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 116,032	$ 116,032	$ 118,373
Accumulated Amortization	(29,054)	(29,054)	(22,456)
Total	86,978	86,978	95,917
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	95,711	95,711	95,711
Accumulated Amortization	(20,384)	(20,384)	(13,326)
Total	75,327	$ 75,327	$ 82,385
Amortization Period		10 years	10 years
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	15,281	$ 15,281	$ 17,561
Accumulated Amortization	(6,281)	(6,281)	(7,416)
Total	9,000	$ 9,000	$ 10,145
Customer relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization Period		7 years	7 years
Customer relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization Period		15 years	15 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	221	$ 221	$ 221
Accumulated Amortization	(179)	(179)	(146)
Total	42	$ 42	$ 75
Amortization Period		5 years	5 years
Loan servicing rights
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	4,819	$ 4,819	$ 4,880
Accumulated Amortization	(2,210)	(2,210)	(1,568)
Total	2,609	2,609	3,312
Impairment loss	$ (100)	$ 300	$ 500
Loan servicing rights | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization Period		10 years	10 years
Loan servicing rights | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization Period		25 years	25 years