PENSION BENEFITS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Change in benefit obligations:
Service cost	$ 2,615	$ 2,234	$ 7,845	$ 6,702
Interest cost	2,588	2,339	7,764	7,017
Recognized prior service cost	(179)	(192)	(538)	(576)
Components of net periodic benefit cost:
Service cost	2,615	2,234	7,845	6,702
Interest cost	2,588	2,339	7,764	7,017
Expected return on assets	(2,694)	(2,634)	(8,081)	(7,902)
Amortization of unrecognized transition amount		5		15
Recognized prior service cost	(179)	(192)	(538)	(576)
Recognized net loss	1,976	926	5,928	2,778
Net periodic benefit cost	$ 4,306	$ 2,678	$ 12,918	$ 8,034