Condensed Consolidated Balance Sheets Parenthetical (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Allowance for receivables	$ 12,400,000	$ 13,300,000
Preferred Stock, Shares Authorized	2,357,299	2,357,299
Preferred Stock, 6 3/4% Cumulative Convertible, Shares Issued	155,250	155,250
Preferred Stock, 6 3/4% Cumulative Convertible, Shares Outstanding	155,250	155,250
Preferred Stock, Depositary Shares	3,105,000	3,105,000
Preferred Stock, Dividend Rate, Percentage	6.75%	6.75%
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000
Preferred Stock Liquidation Depositary Per Share	$ 50	$ 50
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	480,000,000	480,000,000
Common Stock, Shares, Issued	208,450,336	202,960,430
Common Stock, Shares, Outstanding	207,928,616	202,468,710