Schedule II - 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]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of year	$ 24,868	$ 26,648	$ 25,060
Additions	10,928	13,849	16,727
Deductions	13,668	15,629	15,139
Balance at end of year	$ 22,128	$ 24,868	$ 26,648