SHORT-TERM BORROWINGS AND LONG-TERM OBLIGATIONS (Details) (USD $) In Thousands, unless otherwise specified			0 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Jan. 19, 2013 8.375% senior notes	Dec. 21, 2012 8.375% senior notes	Apr. 23, 2012 8.375% senior notes	Jul. 31, 2011 8.375% senior notes	Dec. 31, 2012 8.375% senior notes	Dec. 31, 2011 8.375% senior notes	Dec. 21, 2011 8.375% senior notes	Jul. 31, 2011 Credit Agreement	Dec. 31, 2012 Credit Agreement	Mar. 31, 2013 Credit Agreement	Dec. 31, 2011 Credit Agreement	Jun. 30, 2011 Credit Agreement	Dec. 31, 2010 Credit Agreement	Mar. 31, 2013 Credit Agreement Maturity by December 2013	Mar. 31, 2013 Credit Agreement Maturity by December 2015	Dec. 31, 2012 Letters of credit	Dec. 31, 2011 Letters of credit
SHORT-TERM BORROWINGS AND LONG-TERM OBLIGATIONS
Long-term obligations	$ 250,000	$ 250,000					$ 250,000	$ 250,000
Interest rate (as a percent)						8.375%	8.375%
Aggregate principal amount						250,000
Price of notes as percentage of principal amount						100.00%
Transaction costs						9,100
Aggregate principal amount of notes exchanged for notes registered under the Securities Act									250,000
Increase in per annum interest rate (as a percent)			0.005	0.005	0.0025
Additional interest per annum			1,250	1,250	625
Aggregate additional interest per annum							3,125
Unamortized deferred financing fees	8,074	10,290					7,205	8,552			869		1,738
Maximum borrowings											129,500	75,000	129,500	200,000	129,500	18,750	56,250	50,000	50,000
Annualized rate of interest											one-month LIBOR
Repayment of outstanding amounts with net proceeds from the Offering										135,319
Available borrowing capacity																		$ 50,000	$ 50,000