SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (Details) (Allowance for doubtful accounts, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Allowance for doubtful accounts
Movement in valuation and qualifying accounts
Balance at Beginning of Period	$ 12,550	$ 10,945	$ 8,492
Charged to costs and expenses	2,236	3,683	4,099
Deductions	(2,211)	(2,078)	(1,646)
Balance at End of Period	$ 12,575	$ 12,550	$ 10,945