Consolidated Statement Of Changes In Equity (USD $) In Thousands	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Dividends In Excess Of Net Earnings [Member]	Noncontrolling Interests In Subsidiaries [Member]	Total
Balance, value at Dec. 31, 2010	$ 25,000	$ 796	$ 2,292,641	$ (560,165)	$ 285,665	$ 2,043,937
Balance, shares at Dec. 31, 2010	10	79,605
Net income				55,226	7,723	62,949
Preferred stock dividends				(1,664)		(1,664)
Common stock dividends				(117,507)		(117,507)
Common unit distributions					(17,305)	(17,305)
Common stock offering, value		72	227,302			227,374
Common stock offering, shares		7,188
Decrease in noncontrolling interest					(107)	(107)
Redemption of common units for common stock, value		2	5,189		(5,191)
Redemption of common units for common stock, shares		237
Shares issued under Dividend Reinvestment and Stock Purchase Plan, value			139			139
Shares issued under Dividend Reinvestment and Stock Purchase Plan, shares		4
Stock options exercised, value		1	3,047			3,048
Stock options exercised, shares		108
Stock compensation			2,393			2,393
Accrued redemption of preferred stock	(25,000)		164			(24,836)
Rebalancing of ownership percent between parent and subsidiaries			(9,438)		9,438
Balance, value at Sep. 30, 2011		$ 871	$ 2,521,437	$ (624,110)	$ 280,223	$ 2,178,421
Balance, shares at Sep. 30, 2011	10	87,142