INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,380,438	$ 1,198,976
Gross Unrealized Gains	24,261	6,257
Gross Unrealized Losses	(1,296)	(12,810)
Estimated Fair Value	1,403,403	1,192,423
U.S. government sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	22,246
Gross Unrealized Gains	116
Gross Unrealized Losses	0
Estimated Fair Value	22,362
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	102,952	149,670
Gross Unrealized Gains	2,310	1,367
Gross Unrealized Losses	(2)	(304)
Estimated Fair Value	105,260	150,733
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	51,720	67,123
Gross Unrealized Gains	1,281	718
Gross Unrealized Losses	(2)	(527)
Estimated Fair Value	52,999	67,314
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	73,704	79,410
Gross Unrealized Gains	617	183
Gross Unrealized Losses	(409)	(1,789)
Estimated Fair Value	73,912	77,804
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,129,816	902,773
Gross Unrealized Gains	19,937	3,989
Gross Unrealized Losses	(883)	(10,190)
Estimated Fair Value	$ 1,148,870	$ 896,572

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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