FAIR VALUES OF FINANCIAL INSTRUMENTS: (Details 4) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Carrying amount and estimated fair value of financial instruments
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 7,132	$ 13,974	$ 13,995	$ 14,050
Securities available-for-sale	814,931	853,725
Restricted Stock	10,379	10,359
Accrued interest receivable	12,913	12,311
Deposits	(2,458,653)	(2,428,526)
Level 1
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	20,682	21,047
Securities available-for-sale	0	0
Level 2
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	53,425	53,965
Federal funds sold		6,952
Securities available-for-sale	796,646	837,147
Accrued interest receivable	3,596	3,340
Deposits	(2,456,900)	(2,414,555)
Short-term borrowings	(57,686)	(80,989)
Federal Home Loan Bank advances	0	(137)
Accrued interest payable	(372)	(363)
Level 3
Carrying amount and estimated fair value of financial instruments
Securities available-for-sale	18,285	16,578
Loans, net	1,878,166	1,854,046
Accrued interest receivable	9,317	8,971
Reported Value Measurement [Member]
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	74,107	75,012
Federal funds sold		6,952
Securities available-for-sale	814,931	853,725
Restricted Stock	10,379	10,359
Loans, net	1,886,852	1,820,407
Accrued interest receivable	12,913	12,311
Deposits	(2,458,653)	(2,428,526)
Short-term borrowings	(57,686)	(80,989)
Federal Home Loan Bank advances	0	(132)
Accrued interest payable	(372)	(363)
Estimate of Fair Value Measurement [Member]
Carrying amount and estimated fair value of financial instruments
Cash and due from banks	74,107	75,012
Federal funds sold		6,952
Securities available-for-sale	814,931	853,725
Loans, net	1,878,166	1,854,046
Accrued interest receivable	12,913	12,311
Deposits	(2,456,900)	(2,414,555)
Short-term borrowings	(57,686)	(80,989)
Federal Home Loan Bank advances	0	(137)
Accrued interest payable	$ (372)	$ (363)

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
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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