Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Lease income	$ 980,166	$ 1,094,301	$ 1,083,770
Other property income	9,508	9,201	8,711
Management, transaction, and other fees	26,501	29,636	28,494
Total revenues	1,016,175	1,133,138	1,120,975
Operating expenses:
Depreciation and amortization	345,900	374,283	359,688
Operating and maintenance	170,073	169,909	168,034
General and administrative	75,001	74,984	65,491
Real estate taxes	143,004	136,236	137,856
Other operating expenses	12,642	7,814	9,737
Total operating expenses	746,620	763,226	740,806
Other expense (income):
Interest expense, net	156,678	151,264	148,456
Goodwill impairment	132,128	0	0
Provision for impairment of real estate, net of tax	18,536	54,174	38,437
Gain on sale of real estate, net of tax	(67,465)	(24,242)	(28,343)
Early extinguishment of debt	21,837	11,982	11,172
Net investment (income) loss	(5,307)	(5,568)	1,096
Total other expense (income)	256,407	187,610	170,818
Income from operations before equity in income of investments in real estate partnerships	13,148	182,302	209,351
Equity in income of investments in real estate partnerships (note 4)	34,169	60,956	42,974
Net income	47,317	243,258	252,325
Noncontrolling interests:
Exchangeable operating partnership units	(203)	(634)	(525)
Limited partners’ interests in consolidated partnerships	(2,225)	(3,194)	(2,673)
Income attributable to noncontrolling interests	(2,428)	(3,828)	(3,198)
Net income attributable to common stockholders	$ 44,889	$ 239,430	$ 249,127
Income per common share - basic (note 15)	$ 0.27	$ 1.43	$ 1.47
Income per common share - diluted (note 15)	$ 0.26	$ 1.43	$ 1.46
Partnership Interest [Member]
Revenues:
Lease income	$ 980,166	$ 1,094,301	$ 1,083,770
Other property income	9,508	9,201	8,711
Management, transaction, and other fees	26,501	29,636	28,494
Total revenues	1,016,175	1,133,138	1,120,975
Operating expenses:
Depreciation and amortization	345,900	374,283	359,688
Operating and maintenance	170,073	169,909	168,034
General and administrative	75,001	74,984	65,491
Real estate taxes	143,004	136,236	137,856
Other operating expenses	12,642	7,814	9,737
Total operating expenses	746,620	763,226	740,806
Other expense (income):
Interest expense, net	156,678	151,264	148,456
Goodwill impairment	132,128	0	0
Provision for impairment of real estate, net of tax	18,536	54,174	38,437
Gain on sale of real estate, net of tax	(67,465)	(24,242)	(28,343)
Early extinguishment of debt	21,837	11,982	11,172
Net investment (income) loss	(5,307)	(5,568)	1,096
Total other expense (income)	256,407	187,610	170,818
Income from operations before equity in income of investments in real estate partnerships	13,148	182,302	209,351
Equity in income of investments in real estate partnerships (note 4)	34,169	60,956	42,974
Net income	47,317	243,258	252,325
Noncontrolling interests:
Limited partners’ interests in consolidated partnerships	(2,225)	(3,194)	(2,673)
Income attributable to noncontrolling interests	(2,225)	(3,194)	(2,673)
Net income attributable to common unit holders	$ 45,092	$ 240,064	$ 249,652
Income per common unit - basic (note 15):	$ 0.27	$ 1.43	$ 1.47
Income per common unit - diluted (note 15):	$ 0.26	$ 1.43	$ 1.46