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SECURITIES - Narrative (Details)		3 Months Ended								12 Months Ended
SECURITIES - Narrative (Details)	Jan. 01, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Investments, Debt Securities [Abstract]
Proceeds from sale of held-to-maturity securities										$ 0	$ 0	$ 0
Investment [Line Items]
Transferred Securities, Unrealized Loss, Before Tax		$ 3,700,000				$ 15,300,000				3,700,000	15,300,000
Securities transferred, Unrealized Loss, Net of Tax		2,900,000				12,100,000				2,900,000	12,100,000
Fair value of securities transferred from AFS to HTM										0	0
Less than 12 Months, fair value		273,963,000				115,902,000				273,963,000	115,902,000
More than 12 Months, fair value		$ 30,697,000				1,345,243,000				$ 30,697,000	1,345,243,000
AFS securities and HTM securities with other-than-temporary impairment		0								0
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net gain (loss) on sale of securities available for sale		$ 42,000	$ 42,000	$ 416,000	$ 256,000	61,000	$ (741,000)	$ (332,000)	$ (827,000)	$ 756,000	(1,839,000)
Gross realized gains on AFS securities										5,700,000	2,000,000.0
Gross realized loss on AFS securities										4,900,000	3,800,000
Net realized gain (loss) on AFS securities												625,000
Gross realized gains on AFS securities												5,000,000.0
Gross realized loss on AFS securities												4,400,000
Carrying value of investment securities pledged as collateral		1,120,000,000				1,080,000,000.00				1,120,000,000	1,080,000,000.00
Equity investments		$ 12,331,000				$ 12,093,000				$ 12,331,000	$ 12,093,000
Equity investments with other-than-temporary impairment		0								0
Federal Home Loan Bank stock with other-than-temporary impairment		0								0
Accounting Standards Update 2017-08
Investment [Line Items]
Cumulative effect of ASU 2017-08, pre-tax	$ (16,500,000)
Equity investments
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Unrealized losses on equity investment included in AFS securities												$ 85,000