ALLOWANCE FOR LOAN LOSSES: (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Allowance for Loan Losses:
Beginning balance	$ 18,773		$ 19,946		$ 18,839
Provision for loan losses	5,295	[1]	3,300	[2]	4,700	[3]
Loans charged -off	(8,762)		(8,949)		(8,528)
Recoveries	4,603		4,476		4,935
Ending Balance	19,909		18,773		19,946
Commercial
Allowance for Loan Losses:
Beginning balance	9,731		11,482		10,915
Provision for loan losses	745	[1]	(755)	[2]	990	[3]
Loans charged -off	(1,572)		(2,659)		(2,852)
Recoveries	1,377		1,663		2,429
Ending Balance	10,281		9,731		11,482
Residential
Allowance for Loan Losses:
Beginning balance	1,553		1,834		1,374
Provision for loan losses	(179)	[1]	54	[2]	874	[3]
Loans charged -off	(761)		(1,011)		(866)
Recoveries	842		676		452
Ending Balance	1,455		1,553		1,834
Consumer
Allowance for Loan Losses:
Beginning balance	5,767		4,945		4,370
Provision for loan losses	4,987	[1]	3,964	[2]	3,331	[3]
Loans charged -off	(6,429)		(5,279)		(4,810)
Recoveries	2,384		2,137		2,054
Ending Balance	6,709		5,767		4,945
Unallocated
Allowance for Loan Losses:
Beginning balance	1,722		1,685		2,180
Provision for loan losses	(258)	[1]	37	[2]	(495)	[3]
Loans charged -off	0		0		0
Recoveries	0		0		0
Ending Balance	$ 1,464		$ 1,722		$ 1,685

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