RETIREMENT PLANS: (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Service cost - benefits earned	$ 1,218	$ 1,388	$ 1,432
Interest cost on projected benefit obligation	3,465	3,194	3,621
Expected return on plan assets	(3,585)	(3,962)	(3,940)
Net amortization and deferral	1,558	1,448	1,205
Net periodic pension cost	2,656	2,068	2,318
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)
Total recognized net periodic pension cost and other comprehensive income	$ 7,459	$ (572)	$ 6,479