INVESTMENTS (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Abstract]
Fair Value	$ 1,399,823	$ 1,115,813
Obligations of U.S. government sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	7,200
Unrealized Gains	2
Unrealized Losses	(119)
Fair Value	7,083
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	112,792	119,608
Unrealized Gains	6,116	7,627
Unrealized Losses	(255)	(115)
Fair Value	118,653	127,120
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	829,611	547,396
Unrealized Gains	13,290	19,796
Unrealized Losses	(3,360)	(574)
Fair Value	839,541	566,618
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	423,244	399,937
Unrealized Gains	5,782	10,652
Unrealized Losses	(3,724)	(135)
Fair Value	425,302	410,454
Subordinated corporate bonds
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,017	11,533
Unrealized Gains	245	186
Unrealized Losses	(18)	(98)
Fair Value	9,244	11,621
Total AFS debt securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,381,864	1,078,474
Unrealized Gains	25,435	38,261
Unrealized Losses	(7,476)	(922)
Fair Value	$ 1,399,823	$ 1,115,813

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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