RETIREMENT PLANS: (Details 7) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain) during the period	$ (6,150)	$ (1,894)	$ 23,111
Amortization of prior service cost	(1)	(1)	9
Amortization of unrecognized gain (loss)	(1,935)	(2,064)	(759)
Total recognized in other comprehensive income (loss)	(8,086)	(3,959)	12,537
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss (gain) during the period	(511)	(255)	932
Amortization of prior service cost	0	0	0
Amortization of unrecognized gain (loss)	(57)	(88)	(7)
Total recognized in other comprehensive income (loss)	$ (568)	$ (343)	$ 925