INVESTMENT SECURITIES - Summary of Unrealized Loss Positions (Details)	3 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($)
Investments in an unrealized loss position
Amount of pretax loss if securities in an unrealized loss position are sold		$ (937,000)
Investments in an Unrealized Loss Position
Less than 12 months, fair value		31,931,000	$ 20,510,000
Less than 12 months, unrealized loss		(276,000)	(249,000)
12 months or more, fair value		43,725,000	148,468,000
12 months or more, unrealized loss		(661,000)	(4,675,000)
Sales of investment securities available-for-sale		31,220,000	2,743,000	$ 53,198,000
Gains on the sale of investments		105,000	352,000	1,100,000
Losses on the sale of investments		271,000	25,000	372,000
Sale of equity investments		6,000,000.0	0	0
Gain on sale of equity investments		0	0	0
Loss on sale of equity investments		7,000	0	0
Unrealized holding gains on equity securities	$ 13,500,000	13,800,000	0	0
Holding losses on equity securities		0	590,000	0
Sales of investment securities		$ 0	$ 0	$ 0
U. S. Agency securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security		26	54
Investments in an Unrealized Loss Position
Less than 12 months, fair value		$ 8,160,000	$ 9,762,000
Less than 12 months, unrealized loss		(59,000)	(123,000)
12 months or more, fair value		15,399,000	63,740,000
12 months or more, unrealized loss		$ (190,000)	$ (1,502,000)
U.S. Sponsored Mortgage-backed securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security		40	42
Investments in an Unrealized Loss Position
Less than 12 months, fair value		$ 16,660,000	$ 2,360,000
Less than 12 months, unrealized loss		(170,000)	(32,000)
12 months or more, fair value		27,498,000	47,755,000
12 months or more, unrealized loss		$ (454,000)	$ (2,007,000)
Municipal securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security		13	78
Investments in an Unrealized Loss Position
Less than 12 months, fair value		$ 6,018,000	$ 5,936,000
Less than 12 months, unrealized loss		(40,000)	(46,000)
12 months or more, fair value		828,000	35,955,000
12 months or more, unrealized loss		$ (17,000)	$ (1,146,000)
Other securities
Description and Number of Positions
Number of investments in an unrealized loss position, AFS | security		2	2
Investments in an Unrealized Loss Position
Less than 12 months, fair value		$ 1,093,000	$ 2,452,000
Less than 12 months, unrealized loss		(7,000)	(48,000)
12 months or more, fair value		0	1,018,000
12 months or more, unrealized loss		$ 0	$ (20,000)