SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Total AFS securities	$ 1,911,242	$ 971,339
Gross Unrealized Gains	4,560	10,569
Gross Unrealized (Losses)	(32,661)	(7,686)
Estimated Fair Value	1,883,141	974,222
Obligations of States and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Total AFS securities	566,268	295,546
Gross Unrealized Gains	3,380	6,842
Gross Unrealized (Losses)	(6,175)	(564)
Estimated Fair Value	563,473	301,824
Corporate and Other Bonds
Debt Securities, Available-for-sale [Line Items]
Total AFS securities	163,117	113,625
Gross Unrealized Gains	382	1,131
Gross Unrealized (Losses)	(2,007)	(876)
Estimated Fair Value	161,492	113,880
Mortgage-Backed Securities
Debt Securities, Available-for-sale [Line Items]
Total AFS securities	1,170,410	552,431
Gross Unrealized Gains	798	2,596
Gross Unrealized (Losses)	(24,295)	(6,169)
Estimated Fair Value	1,146,913	548,858
Other Securities
Debt Securities, Available-for-sale [Line Items]
Total AFS securities	11,447	9,737
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(184)	(77)
Estimated Fair Value	$ 11,263	$ 9,660

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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-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 50
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-Subparagraph (b)
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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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-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).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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