LONG-TERM DEBT / INTEREST EXPENSE (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Long-term Debt
Total Debt	$ 1,096,923,000		$ 1,096,923,000		$ 1,098,562,000
Less: current maturities	(3,557,000)		(3,557,000)		(3,817,000)
Long-term debt	1,093,366,000		1,093,366,000		1,094,745,000
Interest expense, net	11,101,000	10,495,000	22,116,000	20,878,000
Senior credit facility
Long-term Debt
Total Debt	1,095,366,000		1,095,366,000		1,096,112,000
Term Loan Facility
Long-term Debt
Interest expense, net			22,100,000	20,900,000
Interest rate (as a percent)	3.75%		3.75%		3.75%
Revolving Credit Facility
Long-term Debt
Interest rate (as a percent)	3.00%		3.00%		3.00%
Letter of credit
Long-term Debt
Outstanding letters of credit	1,100,000		1,100,000		1,100,000
Mortgage
Long-term Debt
Total Debt	1,554,000		1,554,000		2,444,000
Capital leases
Long-term Debt
Total Debt	$ 3,000		$ 3,000		$ 6,000