RETIREMENT PLANS: (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Service cost - benefits earned	$ 1,882	$ 2,153	$ 2,040
Interest cost on projected benefit obligation	3,729	3,516	3,756
Expected return on plan assets	(3,429)	(3,452)	(3,794)
Net amortization and deferral	1,936	2,065	750
Net periodic pension cost	4,118	4,282	5,428
Net loss (gain) during the period	(6,150)	(1,894)	23,111
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	0	0
Defined Benefit Plan, Other Changes			(2,676)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	0	0	2,676
Defined Benefit Plan, Settlements, Benefit Obligation	0	0
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)
Total recognized net periodic pension cost and other comprehensive income	$ (3,968)	$ 323	$ 17,965