INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,252,330	$ 1,198,976
Gross Unrealized Gains	22,794	6,257
Gross Unrealized Losses	(1,880)	(12,810)
Estimated Fair Value	1,273,244	1,192,423
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	99,888	149,670
Gross Unrealized Gains	2,148	1,367
Gross Unrealized Losses	(3)	(304)
Estimated Fair Value	102,033	150,733
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	56,876	67,123
Gross Unrealized Gains	1,009	718
Gross Unrealized Losses	(39)	(527)
Estimated Fair Value	57,846	67,314
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,095,566	982,183
Gross Unrealized Gains	19,637	4,172
Gross Unrealized Losses	(1,838)	(11,979)
Estimated Fair Value	$ 1,113,365	$ 974,376

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).

+ References

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-Publisher FASB
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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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-Publisher FASB
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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