Consolidated Statement of Changes in Equity (USD $) In Thousands, unless otherwise specified	Parent Company [Member]	Partnership Interest [Member]	Preferred Stock Parent Company [Member]	Common Stock Parent Company [Member]	Treasury Stock Parent Company [Member]	Additional Paid In Capital Parent Company [Member]	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Parent Company [Member]	Accumulated Other Comprehensive Loss Partnership Interest [Member]	Distributions in Excess of Net Income Parent Company [Member]	Total Stockholders’ Equity Parent Company [Member]	Noncontrolling Interests Preferred Units Parent Company [Member]	Noncontrolling Interest Exchangeable Operating Partnership Units Parent Company [Member]	Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships Parent Company [Member]	Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships Partnership Interest [Member]	Total Noncontrolling Interests Parent Company [Member]	Preferred Units Partnership Interest [Member]	General Partner Preferred and Common Units Partnership Interest [Member]	Limited Partners Partnership Interest [Member]	Total Partners’ Capital Partnership Interest [Member]	Preferred Units Parent Company [Member]	Preferred Units Partnership Interest [Member]	Preferred Units Total Noncontrolling Interests Parent Company [Member]	Preferred Units Total Partners’ Capital Partnership Interest [Member]	Preferred Stock Parent Company [Member]	Preferred Stock Partnership Interest [Member]	Preferred Stock Additional Paid In Capital Parent Company [Member]	Preferred Stock General Partner Preferred and Common Units Partnership Interest [Member]	Preferred Stock Total Partners’ Capital Partnership Interest [Member]	Common Stock Parent Company [Member]	Common Stock Additional Paid In Capital Parent Company [Member]	Common Stock Accumulated Other Comprehensive Loss Parent Company [Member]	Common Stock Distributions in Excess of Net Income Parent Company [Member]	Common Stock Total Stockholders’ Equity Parent Company [Member]	Common Stock Noncontrolling Interests in Limited Partners' Interest in Consolidated Partnerships Parent Company [Member]	Common Stock Total Noncontrolling Interests Parent Company [Member]	Preferred Partner Noncontrolling Interests Preferred Units Parent Company [Member]
Beginning balance at Dec. 31, 2009	$ (1,930,607)	$ (1,930,607)	$ (275,000)	$ (815)	$ 16,509	$ (2,024,883)		$ 49,973	$ 49,973	$ 371,836	$ (1,862,380)	$ (49,158)	$ (7,321)	$ (11,748)	$ (11,748)	$ (68,227)	$ (49,158)	$ (1,912,353)	$ (7,321)	$ (1,918,859)
Stock Issued During Period, Value, Other				3	0								(7,630)																	0	7,627	0	0	7,630	0	(7,630)
Other comprehensive income (loss):
Net income	13,001	13,001	0	0	0	0		0	0	8,816	8,816	3,725	84	376	376	4,185	3,725	8,816	84	12,625
Net current-period other comprehensive income	(30,981)	(30,981)	0	0	0	0		(30,912)	(30,912)	0	(30,912)	0	(69)	0	0	(69)	0	0	(69)	(30,981)
Deferred compensation plan, net	273	(273)	0	0	(334)	607		0	0	0	273	0	0	0	0	0	0	(273)	0	(273)
Restricted stock issued, net of amortization	7,236		0	0	0	7,236		0		0	7,236	0	0	0		0
Stock Redeemed or Called During Period, Value				0	0								0																	(1,374)	(1,374)	0	0	(1,374)	0	0
Common stock issued for dividend reinvestment plan				1	0								0																	1,848	1,847	0	0	1,848	0	0
Contributions from partners	161	161	0	0	0	0		0	0	0	0	0	0	161	161	161	0	0	0	0
Distributions to partners	1,456	(152,423)	0	0	0	0		0	0	0	0	0	0	1,456	(1,456)	1,456	0	(150,499)	(468)	(150,967)
Preferred unit distributions		(23,400)							0						0		(3,725)	(19,675)	0	(23,400)
Restricted stock issued by Parent Company, net of amortization		7,236							0						0		0	7,236	0	7,236
Common units issued as a result of common stock issued by Parent Company, net of repurchases		474							0						0			474	0	474
Common units exchanged for common stock of Parent Company		0							0						0			7,630	(7,630)	0
Cash dividends declared:
Preferred stock/unit	23,400		0			0		0		19,675	19,675	3,725	0	0		3,725
Common stock/unit	150,967			0	0	0		0		150,499	150,499		468	0		468
Ending Balance at Dec. 31, 2010	(1,744,402)	(1,744,402)	(275,000)	(819)	16,175	(2,039,612)		80,885	80,885	533,194	(1,685,177)	(49,158)	762	(10,829)	(10,829)	(59,225)	(49,158)	(1,766,062)	762	(1,733,573)
Other comprehensive income (loss):
Net income	55,788	55,788	0	0	0	0		0	0	51,370	51,370	3,725	103	590	590	4,418	3,725	51,370	103	55,198
Net current-period other comprehensive income	9,485	9,485	0	0	0	0		9,456	9,456	0	9,456	0	20	9	9	29	0	0	20	9,476
Deferred compensation plan, net	(17,843)	(17,843)	0	0	(978)	(16,865)		0	0	0	(17,843)	0	0	0	0	0	0	(17,843)	0	(17,843)
Restricted stock issued, net of amortization	10,659		0	0	0	10,659		0		0	10,659	0	0	0		0
Stock Redeemed or Called During Period, Value				0	0								0																	(1,689)	(1,689)	0	0	(1,689)	0	0
Common stock issued for dividend reinvestment plan				0	0								0																	1,081	1,081	0	0	1,081	0	0
Common stock issued for stock offerings, net of issuance costs				80	0								0																	215,369	215,289	0	0	215,369	0	0
Contributions from partners	2,787	2,787	0	0	0	0		0	0	0	0	0	0	2,787	2,787	2,787	0	0	0	0
Distributions to partners	1,111	(162,671)	0	0	0	0		0	0	0	0	0	0	1,111	(1,111)	1,111	0	(161,236)	(324)	(161,560)
Preferred unit distributions		(23,400)							0						0		(3,725)	(19,675)	0	(23,400)
Restricted stock issued by Parent Company, net of amortization		10,659							0						0		0	10,659	0	10,659
Common units issued as a result of common stock issued by Parent Company, net of repurchases		214,761							0						0			214,761	0	214,761
Cash dividends declared:
Preferred stock/unit	23,400		0		0	0		0		19,675	19,675	3,725	0	0		3,725
Common stock/unit	161,560			0	0	0		0		161,236	161,236		324	0		324
Ending Balance at Dec. 31, 2011	(1,869,654)	(1,869,654)	(275,000)	(899)	15,197	(2,281,817)		71,429	71,429	662,735	(1,808,355)	(49,158)	963	(13,104)	(13,104)	(61,299)	(49,158)	(1,879,784)	963	(1,856,550)
Other comprehensive income (loss):
Net income	26,209	26,209	0	0	0	0		0	0	25,867	25,867	(629)	106	865	865	342	(629)	25,867	106	25,344
Net current-period other comprehensive income	13,711	13,711	0	0	0	0	13,714	13,714	13,714	0	13,714	0	28	(31)	(31)	(3)	0	0	28	13,742
Deferred compensation plan, net	(12)	12	0	0	(273)	261		0	0	0	(12)	0	0	0	0	0	0	12	0	12
Restricted stock issued, net of amortization	11,526		0	0	0	11,526		0		0	11,526	0	0	0		0
Stock Redeemed or Called During Period, Value				0	0								0																	(1,474)	(1,474)	0	0	(1,474)	0	0
Common stock issued for dividend reinvestment plan				0	0								0																	988	988	0	0	988	0	0
Common stock issued for stock offerings, net of issuance costs		313,900	325,000	5	0						313,900		0					313,900		313,900					313,900		(11,100)			21,542	21,537	0	0	21,542	0	0
Preferred Stock Redemption Premium	275,000		275,000			(9,277)				9,277	275,000						(48,125)				48,125	(48,125)	48,125	(48,125)		(275,000)		(275,000)	(275,000)								48,125
Contributions from partners	3,362	3,362	0	0	0	0		0	0	0	0	0	0	3,362	3,362	3,362	0	0	0	0
Distributions to partners	1,001	(166,736)	0	0	0	0		0	0	0	0	0	0	1,001	(1,001)	1,001	0	(165,411)	(324)	(165,735)
Preferred unit distributions		(23,658)							0						0		(404)	(23,254)	0	(23,658)
Restricted stock issued by Parent Company, net of amortization		11,526							0						0		0	11,526	0	11,526
Common units issued as a result of common stock issued by Parent Company, net of repurchases		21,056							0						0			21,056	0	21,056
Cash dividends declared:
Preferred stock/unit	23,658		0		0	0		0		23,254	23,254	404	0	0		404
Common stock/unit	165,735			0	0	0		0		165,411	165,411		324	0		324
Ending Balance at Dec. 31, 2012	$ (1,745,911)	$ (1,745,911)	$ (325,000)	$ (904)	$ 14,924	$ (2,312,310)		$ 57,715	$ 57,715	$ 834,810	$ (1,730,765)	$ 0	$ 1,153	$ (16,299)	$ (16,299)	$ (15,146)	$ 0	$ (1,788,480)	$ 1,153	$ (1,729,612)