DEBT (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	6 Months Ended		12 Months Ended
	Nov. 30, 2009	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
DEBT
Face amount of Series C Note		$ 80,000
Maturity date of Series C Note		Mar. 01, 2012
Borrowing capacity under the line of credit		150,000
Credit agreement initiation date		November 18, 2009
Compliance with debt covenants		As of June 30, 2011, the Company was in compliance with its debt covenants.
Letters of credit outstanding under the line of credit		60
Amount outstanding under the line of credit		0			0
Available line of credit		149,940
Term of the credit agreement (in years)	3
Additional increase in borrowing capacity of the line of credit available at the entity's option		75,000
Number of days prior to the last day of the credit agreement's term that the entity may request an additional increase in the borrowing capacity of the line of credit		180
Unamortized deferred gain on termination of interest rate swaps		1,165				5,079
Reduction in interest expense from amortization of gain on termination of interest rate swaps		824	824
Expected annual reduction in interest expense from amortization of gain on termination of interest rate swaps				$ 1,661
Weighted average effective interest rate on the Note, net of the impact of swaps (as a percent)		4.00%
Interest rate swap activities		The Company has no interest rate swaps outstanding as of June 30, 2011