GOODWILL AND INTANGIBLE ASSETS: (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 10,836	$ 10,836
Accumulated Amortization	9,206	8,727
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross Amount	10,836	10,836
Accumulated Amortization	$ 9,206	$ 8,727