SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Amortized Cost Basis, Total	$ 971,339	$ 947,597
Gross Unrealized Gains	10,569	10,480
Gross Unrealized (Losses)	(7,686)	(11,313)
Available for sale securities, Estimated fair value	974,222	946,764
Obligations of states and political subdivisions
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Amortized Cost Basis, Total	295,546	274,007
Gross Unrealized Gains	6,842	4,962
Gross Unrealized (Losses)	(564)	(3,079)
Available for sale securities, Estimated fair value	301,824	275,890
Corporate bonds
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Amortized Cost Basis, Total	113,625	123,674
Gross Unrealized Gains	1,131	892
Gross Unrealized (Losses)	(876)	(2,786)
Available for sale securities, Estimated fair value	113,880	121,780
Mortgage-backed securities
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Amortized Cost Basis, Total	552,431	536,031
Gross Unrealized Gains	2,596	4,626
Gross Unrealized (Losses)	(6,169)	(5,371)
Available for sale securities, Estimated fair value	548,858	535,286
Other securities
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Available-for-sale Securities, Amortized Cost Basis, Total	9,737	13,885
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(77)	(77)
Available for sale securities, Estimated fair value	$ 9,660	$ 13,808

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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