Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Document Fiscal Year Focus	2014
Other expense (income) [Abstract]
Provision for impairment	$ 1,257	$ 6,000	$ 74,816
Equity in income of investments in real estate partnerships (note 4)	31,270	31,718	23,807
Federal Income Tax Expense (Benefit), Continuing Operations	1,152	0	13,224
Discontinued operations, net (note 3):
Gain on sale of real estate, net of tax	(55,077)	(59,656)	(24,013)
Parent Company [Member]
Revenues:
Minimum rent	390,697	353,833	340,940
Percentage rent	3,488	3,583	3,323
Recoveries from tenants and other income	119,618	106,494	103,155
Total revenues	537,898	489,007	473,929
Management Transaction And Other Fees	24,095	25,097	26,511
Operating expenses:
Depreciation and amortization	147,791	130,630	119,008
Operating and maintenance	77,788	71,018	66,687
General and administrative	60,242	61,234	61,700
Real estate taxes	59,031	53,726	52,911
Other operating expenses	8,496	8,079	7,187
Total operating expenses	353,348	324,687	307,493
Other expense (income) [Abstract]
Interest Expense	109,491	108,966	112,129
Provision for impairment	1,257	6,000	20,316
Early extinguishment of debt	18	32	852
Net investment income, including unrealized losses (gains) of $1,058, $(2,231), and $(888) in 2014, 2013, and 2012, respectively (notes 8 and 14)	9,449	3,257	2,057
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	(18,271)	0	0
Total other expense (income)	83,046	111,741	131,240
Income before equity in income of investments in real estate partnerships and income taxes	101,504	52,579	35,196
Equity in income of investments in real estate partnerships (note 4)	31,270	31,718	23,807
Federal Income Tax Expense (Benefit), Continuing Operations	(996)	0	13,224
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	133,770	84,297	45,779
Discontinued operations, net (note 3):
Operating income (loss)	0	7,332	(43,583)
Gain on sale of operating properties, net of tax	0	57,953	21,855
Income (loss) from discontinued operations	0	65,285	(21,728)
Gain on sale of real estate, net of tax	(55,077)	(1,703)	(2,158)
Net income	188,847	151,285	26,209
Noncontrolling interests:
Net Income (Loss) Attributable to Noncontrolling Interest, Preferred Unit Holders (Deprecated 2013-01-31)	0	0	629
Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Nonredeemable	(319)	(276)	(106)
Noncontrolling Interest in Net Income (Loss) Limited Partnerships, Nonredeemable	(1,138)	(1,205)	(865)
Income attributable to noncontrolling interests	(1,457)	(1,481)	(342)
Net income attributable to the Company	187,390	149,804	25,867
Preferred stock dividends	(21,062)	(21,062)	(32,531)
Net Income (Loss) attributable to Common Stockholders	166,328	128,742	(6,664)
Income (loss) per common share - basic (note 15):
Continuing operations (in dollars per share)	$ 1.80	$ 0.69	$ 0.16
Discontinued operations (in dollars per share)	$ 0.00	$ 0.71	$ (0.24)
Net income attributable to common stockholders (in dollars per share)	$ 1.80	$ 1.40	$ (0.08)
Income (loss) per common share - diluted (note 15):
Continuing operations (in dollars per share)	$ 1.80	$ 0.69	$ 0.16
Discontinued operations (in dollars per share)	$ 0.00	$ 0.71	$ (0.24)
Net income (loss) attributable to common stockholders (in dollars per share)	$ 1.80	$ 1.40	$ (0.08)
Partnership Interest [Member]
Revenues:
Minimum rent	390,697	353,833	340,940
Percentage rent	3,488	3,583	3,323
Recoveries from tenants and other income	119,618	106,494	103,155
Total revenues	537,898	489,007	473,929
Management Transaction And Other Fees	24,095	25,097	26,511
Operating expenses:
Depreciation and amortization	147,791	130,630	119,008
Operating and maintenance	77,788	71,018	66,687
General and administrative	60,242	61,234	61,700
Real estate taxes	59,031	53,726	52,911
Other operating expenses	8,496	8,079	7,187
Total operating expenses	353,348	324,687	307,493
Other expense (income) [Abstract]
Interest Expense	109,491	108,966	112,129
Provision for impairment	1,257	6,000	20,316
Early extinguishment of debt	18	32	852
Net investment income, including unrealized losses (gains) of $1,058, $(2,231), and $(888) in 2014, 2013, and 2012, respectively (notes 8 and 14)	9,449	3,257	2,057
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	(18,271)	0	0
Total other expense (income)	83,046	111,741	131,240
Income before equity in income of investments in real estate partnerships and income taxes	101,504	52,579	35,196
Equity in income of investments in real estate partnerships (note 4)	31,270	31,718	23,807
Federal Income Tax Expense (Benefit), Continuing Operations	(996)	0	13,224
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	133,770	84,297	45,779
Discontinued operations, net (note 3):
Operating income (loss)	0	7,332	(43,583)
Gain on sale of operating properties, net of tax	0	57,953	21,855
Income (loss) from discontinued operations	0	65,285	(21,728)
Gain on sale of real estate, net of tax	(55,077)	(1,703)	(2,158)
Net income	188,847	151,285	26,209
Noncontrolling interests:
Noncontrolling Interest in Net Income (Loss) Limited Partnerships, Nonredeemable	(1,138)	(1,205)	(865)
Income attributable to noncontrolling interests	(1,138)	(1,205)	(865)
Net income attributable to the Company	187,709	150,080	25,344
Preferred unit distributions	(21,062)	(21,062)	(31,902)
Net (loss) income attributable to common unit holders	$ 166,647	$ 129,018	$ (6,558)
Income (loss) per common share - basic (note 15):
Continuing operations (in dollars per share)	$ 1.80	$ 0.69	$ 0.16
Discontinued operations (in dollars per share)	$ 0.00	$ 0.71	$ (0.24)
Net income attributable to common unit holders (in dollars per share)	$ 1.80	$ 1.40	$ (0.08)
Income (loss) per common share - diluted (note 15):
Continuing operations (in dollars per share)	$ 1.80	$ 0.69	$ 0.16
Discontinued operations (in dollars per share)	$ 0.00	$ 0.71	$ (0.24)
Net Income (Loss), Per Outstanding Limited Partnership Unit, Diluted	$ 1.80	$ 1.40	$ (0.08)