INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Estimated Fair Value
Less Than 12 Months	$ 160,820	$ 299,794
12 Months or More	487,574	213,946
Total	648,394	513,740
Unrealized Losses
Less Than 12 Months	(743)	(2,551)
12 Months or More	(12,067)	(4,341)
Total	(12,810)	(6,892)
State, county and municipal securities
Estimated Fair Value
Less Than 12 Months	23,784	33,976
12 Months or More	33,873	4,725
Total	57,657	38,701
Unrealized Losses
Less Than 12 Months	(52)	(115)
12 Months or More	(252)	(48)
Total	(304)	(163)
Corporate debt securities
Estimated Fair Value
Less Than 12 Months	17,291	3,465
12 Months or More	17,952	18,853
Total	35,243	22,318
Unrealized Losses
Less Than 12 Months	(111)	(35)
12 Months or More	(416)	(202)
Total	(527)	(237)
Mortgage-backed securities
Estimated Fair Value
Less Than 12 Months	119,745	262,353
12 Months or More	435,749	190,368
Total	555,494	452,721
Unrealized Losses
Less Than 12 Months	(580)	(2,401)
12 Months or More	(11,399)	(4,091)
Total	$ (11,979)	$ (6,492)