CONSOLIDATED STATEMENTS OF EQUITY (USD $)	Total	Total Stockholders' Equity	Preferred Stock	Common Stock	Capital in Excess of Par Value	Cumulative Net Income	Other	Cumulative Distributions	Non-controlling Interests	Series E Preferred Stock	Series E Preferred Stock Total Stockholders' Equity	Series E Preferred Stock Preferred Stock	Series E Preferred Stock Capital in Excess of Par Value	Series E Preferred Stock Cumulative Distributions	Series F Preferred Stock	Series F Preferred Stock Total Stockholders' Equity	Series F Preferred Stock Preferred Stock	Series F Preferred Stock Capital in Excess of Par Value	Series F Preferred Stock Cumulative Distributions
Balance at Dec. 31, 2008	$ 461,012,000	$ 457,878,000	$ 189,560,000	$ 231,000	$ 321,979,000	$ 533,565,000	$ 735,000	$ (588,192,000)	$ 3,134,000
Balance (in shares) at Dec. 31, 2008			8,042,000	23,136,000
Increase (Decrease) in Stockholders' Equity
Conversion of 8.5% Series E Preferred Stock					22,000							(22,000)
Conversion of 8.5% Series E Preferred Stock (in shares)				2,000								(1,000)
Reclassification adjustment	(345,000)	(345,000)					(345,000)
Stock option exercises	770,000	770,000			770,000
Stock option exercises (in shares)				35,000
Repurchase of stock	(2,016,000)	(2,016,000)	(2,737,000)		95,000			626,000
Repurchase of stock (in shares)			(109,484)	(1,000)											(109,484)
Issue common stock	766,000	766,000			766,000
Issue common stock (in shares)				30,000
Issue restricted stock	1,000			1,000	(1,000)
Issue restricted stock (in shares)				43,000
Net income	44,360,000	44,064,000				44,064,000			296,000
Vested stock options	147,000	147,000			147,000
Vested restricted stock	1,242,000	1,242,000			1,242,000
Non-controlling interests conversion		1,144,000		1,000	1,143,000				(1,144,000)
Non-controlling interests conversion (in shares)	67,294			67,000
Non-controlling interests preferred return	(305,000)								(305,000)
Preferred stock dividends	(15,141,000)	(15,141,000)						(15,141,000)
Common stock cash distributions ($1.68, $1.58 and $1.56 per share for the year ended 2011, 2010 and 2009, respectively)	(36,177,000)	(36,177,000)						(36,177,000)
Balance at Dec. 31, 2009	454,313,000	452,332,000	186,801,000	233,000	326,163,000	577,629,000	390,000	(638,884,000)	1,981,000
Balance (in shares) at Dec. 31, 2009			7,932,000	23,312,000
Increase (Decrease) in Stockholders' Equity
Conversion of 8.5% Series E Preferred Stock				1,000	822,000							(823,000)
Conversion of 8.5% Series E Preferred Stock (in shares)				65,790								(32,895)
Redemption of preferred stock, partial and full	(59,065,000)	(58,942,000)			2,383,000					(123,000)	(123,000)	(123,000)	6,000	(6,000)	(58,942,000)	(58,942,000)	(58,942,000)	2,377,000	(2,377,000)
Redemption of preferred stock, partial and full (in shares)										(4,921)		(4,921)			2,357,686		2,357,686
Reclassification adjustment	(126,000)	(126,000)					(126,000)
Stock option exercises	182,000	182,000			182,000
Stock option exercises (in shares)				11,666
Issue common stock	67,793,000	67,793,000		27,000	67,766,000
Issue common stock (in shares)				2,746,400
Issue restricted stock	2,000			2,000	(2,000)
Issue restricted stock (in shares)				208,591
Net income	46,053,000	45,862,000				45,862,000			191,000
Vested stock options	75,000	75,000			75,000
Vested restricted stock	1,210,000	1,210,000			1,210,000
Non-controlling interests preferred return	(210,000)								(210,000)
Preferred stock dividends	(13,662,000)	(13,662,000)						(13,662,000)
Common stock cash distributions ($1.68, $1.58 and $1.56 per share for the year ended 2011, 2010 and 2009, respectively)	(39,041,000)	(39,041,000)						(39,041,000)
Balance at Dec. 31, 2010	457,522,000	455,560,000	126,913,000	263,000	398,599,000	623,491,000	264,000	(693,970,000)	1,962,000
Balance (in shares) at Dec. 31, 2010			5,536,530	26,345,000
Increase (Decrease) in Stockholders' Equity
Redemption of preferred stock, partial and full	(88,413,000)	(88,413,000)			3,566,000			(3,566,000)							(88,413,000)		(88,413,000)
Redemption of preferred stock, partial and full (in shares)															3,536,530		3,536,530
Reclassification adjustment	(65,000)	(65,000)					(65,000)
Stock option exercises	120,000	120,000			120,000
Stock option exercises (in shares)				5,000
Issue common stock	103,631,000	103,631,000		40,000	103,591,000
Issue common stock (in shares)				3,990,000
Issue restricted stock				0
Issue restricted stock (in shares)				6,000
Net income	49,443,000	49,252,000				49,252,000			191,000
Vested stock options	17,000	17,000			17,000
Vested restricted stock	1,450,000	1,450,000			1,450,000
Non-controlling interests preferred return	(191,000)							0	(191,000)
Preferred stock dividends	(5,512,000)	(5,512,000)						(5,512,000)
Common stock cash distributions ($1.68, $1.58 and $1.56 per share for the year ended 2011, 2010 and 2009, respectively)	(49,292,000)	(49,292,000)						(49,292,000)
Balance at Dec. 31, 2011	$ 468,710,000	$ 466,748,000	$ 38,500,000	$ 303,000	$ 507,343,000	$ 672,743,000	$ 199,000	$ (752,340,000)	$ 1,962,000
Balance (in shares) at Dec. 31, 2011			2,000,000	30,346,000