SHORT-TERM BORROWINGS: (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase-agreements	$ 27,521	$ 31,007
Average amount outstanding	39,704	37,949
Maximum amount outstanding at a month end	$ 85,714	$ 80,989
Average interest rate during year (percent)	0.62%	0.35%
Interest rate at year-end (percent)	0.96%	0.64%
Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase-agreements	$ 758	$ 758
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase-agreements	8,552	9,516
Maturity up to 30 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase-agreements	6,282	9,495
Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase-agreements	$ 11,929	$ 11,238