EMPLOYEE RETIREMENT PLANS (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 3,303,199	$ 3,070,032	$ 9,909,597	$ 9,289,516
Interest cost	1,914,009	2,200,255	5,742,028	6,614,093
Expected return on plan assets	(4,287,616)	(3,731,362)	(12,862,847)	(11,194,084)
Amortization of net actuarial loss	1,490,590	1,692,028	4,471,771	5,106,432
Amortization of prior service cost	12,582	72,788	37,747	218,364
Net periodic benefit cost	2,432,764	3,303,741	7,298,296	10,034,321
Company's share of net periodic pension benefit cost	753,329	1,016,552	2,259,987	3,086,582
Entity's share of estimated contributions to employee benefit plan	4,500,000		4,500,000
Postretirement benefit plans [Member]
Components of net periodic benefit cost [Abstract]
Service cost	1,574,979	1,537,530	4,724,937	4,612,590
Interest cost	1,542,971	1,634,209	4,628,913	4,902,629
Expected return on plan assets	(907,750)	(804,794)	(2,723,250)	(2,414,382)
Amortization of net actuarial loss	923,505	1,002,154	2,770,515	3,006,462
Amortization of prior service cost	(622,781)	(532,814)	(1,868,343)	(1,598,442)
Net periodic benefit cost	2,510,924	2,836,285	7,532,772	8,508,857
Company's share of net periodic postretirement benefit cost	727,946	821,794	2,183,838	2,465,388
Entity's share of estimated contributions to employee benefit plan	$ 150,000		$ 150,000