INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,302,666	$ 1,380,438
Gross Unrealized Gains	50,800	24,261
Gross Unrealized Losses	(426)	(1,296)
Estimated Fair Value	1,353,040	1,403,403
U.S. government sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	22,227	22,246
Gross Unrealized Gains	484	116
Gross Unrealized Losses	0	0
Estimated Fair Value	22,711	22,362
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	94,318	102,952
Gross Unrealized Gains	2,785	2,310
Gross Unrealized Losses	0	(2)
Estimated Fair Value	97,103	105,260
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	51,700	51,720
Gross Unrealized Gains	495	1,281
Gross Unrealized Losses	(127)	(2)
Estimated Fair Value	52,068	52,999
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,065,512	1,129,816
Gross Unrealized Gains	45,552	19,937
Gross Unrealized Losses	(181)	(883)
Estimated Fair Value	1,110,883	1,148,870
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	68,909	73,704
Gross Unrealized Gains	1,484	617
Gross Unrealized Losses	(118)	(409)
Estimated Fair Value	$ 70,275	$ 73,912

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).

+ References

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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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