EMPLOYEE BENEFIT PLANS (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
EMPLOYEE BENEFIT PLANS
Service cost - benefits earned during the period		$ 2,708,000	$ 2,561,000	$ 5,416,000	$ 5,122,000
Interest cost on projected benefit obligation		2,553,000	2,604,000	5,106,000	5,208,000
Expected return on plan assets		(2,759,000)	(2,673,000)	(5,518,000)	(5,346,000)
Amortization of prior service cost/(credit)		(95,000)	(95,000)	(190,000)	(190,000)
Amortization of actuarial losses		2,729,000	2,175,000	5,458,000	4,350,000
Total benefit cost		5,136,000	4,572,000	10,272,000	9,144,000
Contribution made by the company to its defined benefit pension plan for the plan year 2013	$ 2,300,000			$ 2,300,000
Adjusted funding target percentage to be maintained				80.00%
Funded status for Pension Benefit Guaranty Corporation reporting purposes to be maintained (as a percent)				80.00%
Age of eligibility for prescription drug benefit				65 years