RETIREMENT PLANS: (Details 11) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,153	$ 2,040	$ 2,238
Interest cost	3,516	3,756	3,383
Recognized actuarial loss	(8,802)	22,274
Net periodic pension cost	4,282	5,428	4,387
Net loss (gain) during the period	(1,894)	23,111	(14,697)
Amortization of prior service cost	(1)	9	16
Total recognized in other comprehensive income (loss)	(3,959)	12,537	(16,772)
Total recognized net periodic pension cost and other comprehensive income	323	17,965	(12,385)
Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	63	53	68
Interest cost	173	175	173
Amortization of transition obligation	0	0	60
Recognized actuarial loss	0	0	0
Net periodic pension cost	236	228	301
Net loss (gain) during the period	(200)	456	(338)
Amortization of prior service cost	0	0	(59)
Total recognized in other comprehensive income (loss)	(200)	456	(397)
Total recognized net periodic pension cost and other comprehensive income	$ 36	$ 684	$ (96)