5. INVESTMENT SECURITIES - Amortized cost and estimated fair value of investment securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Debt securities:
Amortized Cost	$ 262,778	$ 253,104
Gross Unrealized Gains	1,933	2,782
Gross Unrealized Losses	(2,389)	(1,866)
Estimated Fair Value	262,322	254,020
US Government Agencies and Sponsored Agencies
Debt securities:
Amortized Cost	233,956	229,118
Gross Unrealized Gains	1,184	2,150
Gross Unrealized Losses	(2,271)	(1,483)
Estimated Fair Value	232,869	229,785
Obligations of states and political subdivisions
Debt securities:
Amortized Cost	22,281	22,436
Gross Unrealized Gains	528	559
Gross Unrealized Losses	(94)	(383)
Estimated Fair Value	22,715	22,612
Corporate Debt Securities
Debt securities:
Amortized Cost	6,490	1,501
Gross Unrealized Gains	160	18
Gross Unrealized Losses	(24)	0
Estimated Fair Value	0	1,519
Corporate stock
Debt securities:
Amortized Cost	51	49
Gross Unrealized Gains	61	55
Gross Unrealized Losses	0	0
Estimated Fair Value	$ (2,389)	$ 104

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- Definition

This item represents the cost of debt 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 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: 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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- Definition

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

+ References

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 of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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