RETIREMENT PLANS: (Details 7) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain) during the period	$ 3,188	$ 6,362	$ (1,192)
Amortization of prior service cost	(1)	(1)	(1)
Amortization of unrecognized gain (loss)	(1,967)	(1,558)	(1,447)
Total recognized in other comprehensive income (loss)	1,220	4,803	(2,640)
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	1,459	1,357	260
Amortization of prior service cost	0	0	0
Amortization of unrecognized gain (loss)	(246)	(75)	(51)
Total recognized in other comprehensive income (loss)	$ 1,213	$ 1,282	$ 209