INDEBTEDNESS (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Long-term debt
Interest paid		$ 5,400,000	$ 9,800,000	$ 17,000,000
Deferred Financing Fees
Write off of deferred financing fees	500,000	477,000
Debt instrument fees	2,800,000
Deferred financing fees, net of accumulated amortization		2,600,000	900,000
Amortization expense related to the deferred financing fees		600,000	600,000	600,000
Eurocurrency
Long-term debt
Basis spread on variable rate (as a percent)		1.00%
Variable interest rate base		Eurocurrency Rate
Base Rate
Long-term debt
Variable interest rate base		Base Rate
Prime rate
Long-term debt
Variable interest rate base		prime rate
Credit agreement
Long-term debt
Maximum borrowing capacity		450,000,000
Maximum increase in the borrowing capacity that is available to the company, subject to certain limitations and satisfaction of certain conditions		200,000,000
Outstanding letters of credit		6,300,000	3,000,000
Revolving credit facility
Long-term debt
Total		$ 193,000,000	$ 212,000,000
Variable rate (as a percent)		1.96%	1.15%
Revolving credit facility | Federal funds rate
Long-term debt
Basis spread on variable rate (as a percent)		0.50%