EMPLOYEE BENEFIT PLANS (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2006
Savings Plan
Maximum participants' contribution as a percentage of pre-tax compensation	20.00%
Employer's matching contribution for each dollar contributed by the employee	$ 0.75	$ 0.75	$ 0.50
Maximum employer contribution as a percentage of base salary	6.00%	6.00%	4.00%
Company contributions	3,499,000	3,232,000	1,953,000
Pension plans
Pension plan and other postretirement benefits
Accumulated benefit obligations	266,496,000	196,184,000
Fair value of pension plan assets	155,749,000	139,034,000	105,639,000
Expected future benefit payments
2012	3,558,000
2013	4,753,000
2014	5,938,000
2015	7,139,000
2016	8,496,000
2017-2021	65,205,000
Net periodic benefit cost	27,834,000	24,773,000	22,379,000
Unfunded supplemental executive retirement plan
Pension plan and other postretirement benefits
Accumulated benefit obligations	26,060,000	21,767,000
Other Postretirement Plan
Pension plan and other postretirement benefits
Fair value of pension plan assets	26,978,000	21,178,000	15,864,000
Expected future benefit payments
2012	1,280,000
2013	1,484,000
2014	1,684,000
2015	1,887,000
2016	2,052,000
Threshold retirement age for participation in plan on payment of a premium (in years)	58
Life insurance benefit	5,000
Net periodic benefit cost	6,291,000	4,782,000	4,926,000
Regulatory asset related to underfunded postretirement benefit expense				9,790,000
Medicare Part D subsidies
2012	213,000
2013	242,000
2014	276,000
2015	313,000
2016	$ 355,000