RETIREMENT PLANS: (Details 9) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Benefit obligation at January 1	$ 102,791	$ 87,796
Service cost	1,300	1,218	$ 1,388
Interest cost	3,116	3,465	3,194
Actuarial (gain) loss	6,845	14,233
Defined Benefit Plan, Benefit Obligation, Benefits Paid	4,130	3,921
Benefit obligation at December 31	109,922	102,791	87,796
Funded status at December 31	(27,485)	(28,829)
Supplemental Employee Retirement Plans, Defined Benefit
Change in benefit obligation:
Benefit obligation at January 1	3,975	3,420
Service cost	38	34
Interest cost	125	145
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	75	65
Actuarial (gain) loss	238	626
Defined Benefit Plan, Benefit Obligation, Benefits Paid	304	315
Benefit obligation at December 31	4,147	3,975	$ 3,420
Funded status at December 31	$ 4,147	$ 3,975