CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME OF ERP OPERATING LIMITED PARTNERSHIP (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Comprehensive income:
Net income	$ 152,167	$ 133,066
Other comprehensive income - derivative instruments:
Unrealized holding gains arising during the year	3,218	6,082
Accumulated other comprehensive income	3,563	956
Other comprehensive (loss) income - other instruments:
Unrealized holding (losses) gains arising during the period	(36)	146
Comprehensive income	158,912	140,250
Comprehensive income attributable to controlling interests	152,044	134,515
OPERATING PARTNERSHIP
Comprehensive income:
Net income	152,167	133,066
Other comprehensive income - derivative instruments:
Unrealized holding gains arising during the year	3,218	6,082
Accumulated other comprehensive income	3,563	956
Other comprehensive (loss) income - other instruments:
Unrealized holding (losses) gains arising during the period	(36)	146
Other comprehensive (loss)	6,745	7,184
Comprehensive income	158,912	140,250
Comprehensive (income) loss attributable to Noncontrolling Interests - Partially Owned Properties	(450)	40
Comprehensive income attributable to controlling interests	$ 158,462	$ 140,290