RETIREMENT PLANS: (Details 11) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,218	$ 1,388	$ 1,432
Interest cost	3,465	3,194	3,621
Recognized actuarial loss	14,233	(10,618)
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)
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
Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	34	42	53
Interest cost	146	131	172
Amortization of net actuarial loss (gain)	(16)	0	0
Net periodic pension cost	164	173	225
Net loss (gain) during the period	626	(872)	83
Amortization of prior service cost	16	0	0
Total recognized in other comprehensive income (loss)	642	(872)	83
Total recognized net periodic pension cost and other comprehensive income	$ 806	$ (699)	$ 308