Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2015
Other expense (income) [Abstract]
Equity in income of investments in real estate partnerships (note 4)	$ 22,508	$ 31,270	$ 31,718
Federal Income Tax Expense (Benefit), Continuing Operations	(1,604)	1,152	0
Discontinued operations, net (note 3):
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes	35,606	55,077	59,656
Parent Company [Member]
Revenues:
Minimum rent	415,155	390,697	353,833
Percentage rent	3,750	3,488	3,583
Recoveries from tenants and other income	125,295	119,618	106,494
Total revenues	569,763	537,898	489,007
Management Transaction And Other Fees	25,563	24,095	25,097
Operating expenses:
Depreciation and amortization	146,829	147,791	130,630
Operating and maintenance	82,978	77,788	71,018
General and administrative	65,600	60,242	61,234
Real estate taxes	61,855	59,031	53,726
Other operating expenses	7,836	8,496	8,079
Total operating expenses	365,098	353,348	324,687
Other expense (income) [Abstract]
Interest Expense	102,622	109,491	108,966
Provision for impairment	0	1,257	6,000
Early extinguishment of debt	8,239	18	32
Net investment income, including unrealized losses (gains) of $1,734, $1,058, and $(2,231) in 2015, 2014, and 2013, respectively (notes 8 and 14)	625	9,449	3,257
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	0	(18,271)	0
Total other expense (income)	110,236	83,046	111,741
Income from operations before equity in income of investments in real estate partnerships	94,429	101,504	52,579
Equity in income of investments in real estate partnerships (note 4)	22,508	31,270	31,718
Federal Income Tax Expense (Benefit), Continuing Operations	0	(996)	0
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	116,937	133,770	84,297
Discontinued operations, net (note 3):
Operating income	0	0	7,332
Gain on sale of operating properties, net of tax	0	0	57,953
Income from discontinued operations	0	0	65,285
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes	35,606	55,077	1,703
Net income	152,543	188,847	151,285
Noncontrolling interests:
Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Nonredeemable	(240)	(319)	(276)
Noncontrolling Interest in Net Income (Loss) Limited Partnerships, Nonredeemable	(2,247)	(1,138)	(1,205)
Income attributable to noncontrolling interests	(2,487)	(1,457)	(1,481)
Net income attributable to the Company	150,056	187,390	149,804
Preferred stock dividends	(21,062)	(21,062)	(21,062)
Net Income (Loss) attributable to Common Stockholders	$ 128,994	$ 166,328	$ 128,742
Income per common share - basic (note 15):
Continuing operations (in dollars per share)	$ 1.37	$ 1.80	$ 0.69
Discontinued operations (in dollars per share)	0.00	0.00	0.71
Net income attributable to common stockholders (in dollars per share)	1.37	1.80	1.40
Income per common share - diluted (note 15):
Continuing operations (in dollars per share)	1.36	1.80	0.69
Discontinued operations (in dollars per share)	0.00	0.00	0.71
Net income (loss) attributable to common stockholders (in dollars per share)	$ 1.36	$ 1.80	$ 1.40
Partnership Interest [Member]
Revenues:
Minimum rent	$ 415,155	$ 390,697	$ 353,833
Percentage rent	3,750	3,488	3,583
Recoveries from tenants and other income	125,295	119,618	106,494
Total revenues	569,763	537,898	489,007
Management Transaction And Other Fees	25,563	24,095	25,097
Operating expenses:
Depreciation and amortization	146,829	147,791	130,630
Operating and maintenance	82,978	77,788	71,018
General and administrative	65,600	60,242	61,234
Real estate taxes	61,855	59,031	53,726
Other operating expenses	7,836	8,496	8,079
Total operating expenses	365,098	353,348	324,687
Other expense (income) [Abstract]
Interest Expense	102,622	109,491	108,966
Provision for impairment	0	1,257	6,000
Early extinguishment of debt	8,239	18	32
Net investment income, including unrealized losses (gains) of $1,734, $1,058, and $(2,231) in 2015, 2014, and 2013, respectively (notes 8 and 14)	625	9,449	3,257
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	0	(18,271)	0
Total other expense (income)	110,236	83,046	111,741
Income from operations before equity in income of investments in real estate partnerships	94,429	101,504	52,579
Equity in income of investments in real estate partnerships (note 4)	22,508	31,270	31,718
Federal Income Tax Expense (Benefit), Continuing Operations	0	(996)	0
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	116,937	133,770	84,297
Discontinued operations, net (note 3):
Operating income	0	0	7,332
Gain on sale of operating properties, net of tax		0	57,953
Income from discontinued operations	0	0	65,285
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes	35,606	55,077	1,703
Net income	152,543	188,847	151,285
Noncontrolling interests:
Noncontrolling Interest in Net Income (Loss) Limited Partnerships, Nonredeemable	(2,247)	(1,138)	(1,205)
Income attributable to noncontrolling interests	(2,247)	(1,138)	(1,205)
Net income attributable to the Company	150,296	187,709	150,080
Preferred unit distributions	(21,062)	(21,062)	(21,062)
Net (loss) income attributable to common unit holders	$ 129,234	$ 166,647	$ 129,018
Income per common share - basic (note 15):
Continuing operations (in dollars per share)	$ 1.37	$ 1.80	$ 0.69
Discontinued operations (in dollars per share)	0.00	0.00	0.71
Net income attributable to common unit holders (in dollars per share)	1.37	1.80	1.40
Income per common share - diluted (note 15):
Continuing operations (in dollars per share)	1.36	1.80	0.69
Discontinued operations (in dollars per share)	0.00	0.00	0.71
Net Income (Loss), Per Outstanding Limited Partnership Unit, Diluted	$ 1.36	$ 1.80	$ 1.40