GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill recorded	$ 0	$ 35,485,000
Reduction of goodwill recorded	0	(35,000)
Carrying value of intangible assets	13,496,000	17,428,000
Amortization of Intangible Assets	$ 3,932,000	4,376,000	$ 3,741,000
Minimum
Goodwill [Line Items]
Core deposits intangibles amortization period	7 years
Maximum
Goodwill [Line Items]
Core deposits intangibles amortization period	10 years
Jacksonville Bancorp, Inc
Goodwill [Line Items]
Goodwill recorded		35,485,000
Core deposit intangible assets recorded		4,746,000
Merchants
Goodwill [Line Items]
Reduction of goodwill recorded		$ (35,000)