INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Value of Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Estimated Fair Value
Less than 12 months, estimated fair value	$ 31,400	$ 160,820
12 months or more, estimated fair value	203,961	487,574
Total estimated fair value	235,361	648,394
Unrealized Losses
Less than 12 months, unrealized losses	(62)	(743)
12 months or more, unrealized losses	(1,818)	(12,067)
Total unrealized losses	(1,880)	(12,810)
State, county and municipal securities
Estimated Fair Value
Less than 12 months, estimated fair value	0	23,784
12 months or more, estimated fair value	3,830	33,873
Total estimated fair value	3,830	57,657
Unrealized Losses
Less than 12 months, unrealized losses	0	(52)
12 months or more, unrealized losses	(3)	(252)
Total unrealized losses	(3)	(304)
Corporate debt securities
Estimated Fair Value
Less than 12 months, estimated fair value	1,476	17,291
12 months or more, estimated fair value	8,615	17,952
Total estimated fair value	10,091	35,243
Unrealized Losses
Less than 12 months, unrealized losses	(24)	(111)
12 months or more, unrealized losses	(15)	(416)
Total unrealized losses	(39)	(527)
Mortgage-backed securities
Estimated Fair Value
Less than 12 months, estimated fair value	29,924	119,745
12 months or more, estimated fair value	191,516	435,749
Total estimated fair value	221,440	555,494
Unrealized Losses
Less than 12 months, unrealized losses	(38)	(580)
12 months or more, unrealized losses	(1,800)	(11,399)
Total unrealized losses	$ (1,838)	$ (11,979)