RETIREMENT PLANS: (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Service cost - benefits earned	$ 2,153	$ 2,040	$ 2,238
Interest cost on projected benefit obligation	3,516	3,756	3,383
Expected return on plan assets	(3,452)	(3,794)	(3,309)
Net amortization and deferral	2,065	750	2,075
Net periodic pension cost	4,282	5,428	4,387
Net loss (gain) during the period	(1,894)	23,111	(14,697)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	0	(2,676)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	0	2,676	0
Defined Benefit Plan, Settlements, Benefit Obligation	0	(7,148)	0
Amortization of prior service cost	1	(9)	(16)
Amortization of unrecognized gain (loss)	(2,064)	(759)	(2,091)
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)