CONSOLIDATED STATEMENTS OF OPERATIONS OF ERP OPERATING LIMITED PARTNERSHIP (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
REVENUES
Rental income	$ 2,114,142,000	$ 1,874,465,000	$ 1,665,233,000
Fee and asset management	9,573,000	9,026,000	9,476,000
Total revenues	2,123,715,000	1,883,491,000	1,674,709,000
EXPENSES
Property and maintenance	415,986,000	387,968,000	374,135,000
Real estate taxes and insurance	241,876,000	211,518,000	200,779,000
Property management	81,902,000	81,867,000	79,857,000
Fee and asset management	4,663,000	4,279,000	4,998,000
Depreciation	664,082,000	612,579,000	581,469,000
General and administrative	47,248,000	43,605,000	39,881,000
Impairment	0	0	45,380,000
Total expenses	1,455,757,000	1,341,816,000	1,326,499,000
Operating income	667,958,000	541,675,000	348,210,000
Interest and other income	150,547,000	7,965,000	5,118,000
Other expenses	(27,361,000)	(14,292,000)	(11,792,000)
Interest:
Expense incurred, net	457,666,000	464,277,000	460,748,000
Amortization of deferred financing costs	21,370,000	16,766,000	9,576,000
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations	312,108,000	54,305,000	(128,788,000)
Income and other tax (expense) benefit	539,000	728,000	291,000
(Loss) from investments in unconsolidated entities	(14,000)	0	(735,000)
Net gain on sales of unconsolidated entities	0	0	28,101,000
Net gain (loss) on sales of land parcels	0	4,217,000	(1,395,000)
(Loss) income from continuing operations	311,555,000	57,794,000	(103,108,000)
Discontinued operations, net	569,649,000	877,403,000	399,091,000
Net income	881,204,000	935,197,000	295,983,000
Net (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(844,000)	(832,000)	726,000
Net income attributable to controlling interests	841,719,000	893,585,000	283,610,000
ALLOCATION OF NET INCOME:
Premium on redemption of Preference Units	5,152,000	0	0
Earnings per Unit - basic:
Income (loss) from continuing operations available to Common Shares	$ 0.932	$ 0.140	$ (0.393)
Net income available to Units	$ 2.729	$ 2.984	$ 0.952
Weighted average Units outstanding	316,554	308,062	296,527
Earnings per Unit - diluted:
Income (loss) from continuing operations available to Common Shares	$ 0.923	$ 0.138	$ (0.393)
Net income available to Units	$ 2.705	$ 2.950	$ 0.952
Weighted average Units outstanding	319,766	312,065	296,527
OPERATING PARTNERSHIP
REVENUES
Rental income	2,114,142,000	1,874,465,000	1,665,233,000
Fee and asset management	9,573,000	9,026,000	9,476,000
Total revenues	2,123,715,000	1,883,491,000	1,674,709,000
EXPENSES
Property and maintenance	415,986,000	387,968,000	374,135,000
Real estate taxes and insurance	241,876,000	211,518,000	200,779,000
Property management	81,902,000	81,867,000	79,857,000
Fee and asset management	4,663,000	4,279,000	4,998,000
Depreciation	664,082,000	612,579,000	581,469,000
General and administrative	47,248,000	43,605,000	39,881,000
Impairment	0	0	45,380,000
Total expenses	1,455,757,000	1,341,816,000	1,326,499,000
Operating income	667,958,000	541,675,000	348,210,000
Interest and other income	150,547,000	7,965,000	5,118,000
Other expenses	(27,361,000)	(14,292,000)	(11,792,000)
Interest:
Expense incurred, net	(457,666,000)	(464,277,000)	(460,748,000)
Amortization of deferred financing costs	(21,370,000)	(16,766,000)	(9,576,000)
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations	312,108,000	54,305,000	(128,788,000)
Income and other tax (expense) benefit	(539,000)	(728,000)	(291,000)
(Loss) from investments in unconsolidated entities	(14,000)	0	(735,000)
Net gain on sales of unconsolidated entities	0	0	28,101,000
Net gain (loss) on sales of land parcels	0	4,217,000	(1,395,000)
(Loss) income from continuing operations	311,555,000	57,794,000	(103,108,000)
Discontinued operations, net	569,649,000	877,403,000	399,091,000
Net income	881,204,000	935,197,000	295,983,000
Net (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(844,000)	(832,000)	726,000
Net income attributable to controlling interests	880,360,000	934,365,000	296,709,000
ALLOCATION OF NET INCOME:
Preference Units	10,355,000	13,865,000	14,368,000
Premium on redemption of Preference Units	5,152,000	0	0
General Partner	826,212,000	879,720,000	269,242,000
Limited Partners	38,641,000	40,780,000	13,099,000
Net income available to Units	$ 864,853,000	$ 920,500,000	$ 282,341,000
Earnings per Unit - basic:
Income (loss) from continuing operations available to Common Shares	$ 0.932	$ 0.140	$ (0.393)
Net income available to Units	$ 2.729	$ 2.984	$ 0.952
Weighted average Units outstanding	316,554	308,062	296,527
Earnings per Unit - diluted:
Income (loss) from continuing operations available to Common Shares	$ 0.923	$ 0.138	$ (0.393)
Net income available to Units	$ 2.705	$ 2.950	$ 0.952
Weighted average Units outstanding	319,766	312,065	296,527