INVESTMENTS (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total	$ 864,600	$ 1,508,981
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)	788,123	1,507,486
US Government-sponsored Enterprises Debt Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total		8,585
Unrealized Gains		0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		241
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)		8,344
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total	54,004	112,086
Unrealized Gains	62	5,392
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	320	0
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)	53,746	117,478
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total	642,019	1,003,869
Unrealized Gains	91	7,856
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	65,644	11,468
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)	576,466	1,000,257
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total	145,457	361,781
Unrealized Gains	3	2,835
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	8,890	5,767
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)	136,570	358,849
Subordinated corporate bonds
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total	23,120	22,660
Unrealized Gains	35	152
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,814	254
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)	21,341	22,558
Total AFS debt securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost, Total	864,600	1,508,981
Unrealized Gains	191	16,235
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	76,668	17,730
Available-for-sale securities, at fair value (amortized cost of $864,600 and $1,508,981, respectively)	$ 788,123	$ 1,507,486

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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