RETIREMENT PLANS: (Details 7) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain) during the period	$ 6,362	$ (1,192)	$ 5,366
Amortization of prior service cost	(1)	(1)	(1)
Amortization of unrecognized gain (loss)	(1,558)	(1,447)	(1,204)
Total recognized in other comprehensive income (loss)	4,803	(2,640)	4,161
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain) during the period	1,357	260	527
Amortization of prior service cost	0	0	0
Amortization of unrecognized gain (loss)	(75)	(51)	0
Total recognized in other comprehensive income (loss)	$ 1,282	$ 209	$ 527