INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Federal
Current	$ 7,413,000	$ 4,027,000	$ 10,105,000
Deferred	12,982,000	15,730,000	12,056,000
Total	20,395,000	19,757,000	22,161,000
State
Current	2,629,000	3,020,000	4,382,000
Deferred	142,000	1,779,000	819,000
Total	2,771,000	4,799,000	5,201,000
Total income tax expense
Current	10,042,000	7,047,000	14,487,000
Deferred	13,124,000	17,509,000	12,875,000
Total	23,166,000	24,556,000	27,362,000
Reduction in tax obligation, net of federal income taxes	1,600,000
Current federal tax rate (as a percent)	35.00%
Deferred tax liability bonus depreciation	10,500,000	6,601,000
Reconciliation of the income tax expense computed by applying the current federal tax rate to pretax book income and the amount shown in the Consolidated Statements of Income
Computed expected tax expense	21,308,000	21,774,000	23,771,000
Increase (reduction) in taxes due to:
State income taxes net of federal tax benefit	3,500,000	3,577,000	3,903,000
Investment tax credits	(74,000)	(74,000)	(32,000)
Other	(1,568,000)	(721,000)	(280,000)
Total	23,166,000	24,556,000	27,362,000
Qualified US production activities deduction rate of taxable income (as a percent)	9.00%	9.00%	6.00%
Qualified US production activities deduction rate of taxable gross wages (as a percent)	50.00%	50.00%	50.00%
Reduction in income tax provision as a result of QPAD	$ 490,000	$ 420,000	$ 560,000