SCHEDULE II-VALUATION AND QUALIFYING ACCOUNTS (Details) (Allowance for doubtful accounts, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for doubtful accounts
VALUATION AND QUALIFYING ACCOUNTS
Balance at the beginning of Period	$ 9,738	$ 9,394	$ 8,672
Charged to Costs and Expenses	11,095	8,879	8,641
Net (Deductions) Recoveries	(9,372)	(8,535)	(7,919)
Balance at the end of Period	$ 11,461	$ 9,738	$ 9,394