RETIREMENT PLANS: (Details 11) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,882	$ 2,153	$ 2,040
Interest cost	3,729	3,516	3,756
Recognized actuarial loss	2,839	(8,802)
Net periodic pension cost	4,118	4,282	5,428
Net loss (gain) during the period	(6,150)	(1,894)	23,111
Amortization of prior service cost	(1)	(1)	9
Total recognized in other comprehensive income (loss)	(8,086)	(3,959)	12,537
Total recognized net periodic pension cost and other comprehensive income	(3,968)	323	17,965
Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	55	63	53
Interest cost	186	173	175
Amortization of transition obligation	0	0	0
Recognized actuarial loss	0	0	0
Net periodic pension cost	241	236	228
Net loss (gain) during the period	(144)	(200)	456
Amortization of prior service cost	0	0	0
Total recognized in other comprehensive income (loss)	(144)	(200)	456
Total recognized net periodic pension cost and other comprehensive income	$ 97	$ 36	$ 684