RETIREMENT PLANS: (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Defined Benefit Plan, Benefit Obligation, Benefits Paid	$ 4,130	$ 3,921
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
Benefits paid	(4,130)	(3,921)
Benefit obligation at December 31	109,922	102,791	87,796
Reconciliation of fair value of plan assets:
Fair value of plan assets at January 1	73,962	64,335
Actual return on plan assets	7,856	11,456
Employer contributions	4,749	2,092
Fair value of plan assets at December 31	82,437	73,962	$ 64,335
Funded status at December 31 (plan assets less benefit obligation)	$ (27,485)	$ (28,829)