INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,188,585	$ 1,380,438
Gross Unrealized Gains	50,647	24,261
Gross Unrealized Losses	(336)	(1,296)
Estimated Fair Value	1,238,896	1,403,403
U.S. government sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,207	22,246
Gross Unrealized Gains	474	116
Gross Unrealized Losses	0	0
Estimated Fair Value	17,681	22,362
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	90,012	102,952
Gross Unrealized Gains	3,186	2,310
Gross Unrealized Losses	0	(2)
Estimated Fair Value	93,198	105,260
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	51,680	51,720
Gross Unrealized Gains	701	1,281
Gross Unrealized Losses	(68)	(2)
Estimated Fair Value	52,313	52,999
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	67,241	73,704
Gross Unrealized Gains	2,815	617
Gross Unrealized Losses	(114)	(409)
Estimated Fair Value	69,942	73,912
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	962,445	1,129,816
Gross Unrealized Gains	43,471	19,937
Gross Unrealized Losses	(154)	(883)
Estimated Fair Value	$ 1,005,762	$ 1,148,870

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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