EMPLOYEE RETIREMENT PLANS (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 3,425,478	$ 3,369,584
Interest cost	1,910,241	2,200,125
Expected return on plan assets	(4,287,616)	(3,731,361)
Amortization of net actuarial loss	1,466,085	1,668,760
Amortization of prior service cost	12,582	72,788
Net periodic benefit cost	2,526,770	3,579,896
Net periodic pension benefit cost	781,531	1,099,398
Entity's share of estimated contributions to employee benefit plan	4,500,000
Postretirement benefit plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost	1,574,979	1,537,530
Interest cost	1,542,971	1,634,210
Expected return on plan assets	(907,750)	(804,794)
Amortization of net actuarial loss	923,505	1,002,154
Amortization of prior service cost	(622,781)	(532,814)
Net periodic benefit cost	2,510,924	2,836,286
Net periodic postretirement benefit cost	727,946	821,796
Entity's share of estimated contributions to employee benefit plan	$ 1,200,000