Valuation and Qualifying Accounts (Details) (Allowance for Doubtful Accounts [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Allowance for Doubtful Accounts [Member]
Allowance for uncollectible accounts
Balance at the beginning of the period	$ 13,801	$ 13,015	$ 11,025
Charged to Costs and Expenses	6,742	7,366	7,048
Charged to other Accounts	0	0	0
Write-offs	(6,178)	(7,237)	(5,505)
Other	613	657	447
Balance at the End of the period	$ 14,978	$ 13,801	$ 13,015