Unconsolidated Real Estate Joint Ventures (Unaudited Condensed Financial Information) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Long-term debt	$ 1,154,295				$ 1,191,179				$ 1,154,295	$ 1,191,179
Note payable to EPR	0				0				0	0
Net income	37,968	35,563	2	41,733	34,175	35,043	14,748	29,091	115,266	113,055	(11,906)
Atlantic-EPR I [Member]
Rental properties, net	26,024				26,668				26,024	26,668	27,313
Cash	940				1				940	1	141
Long-term debt	0				0				0	0	15,001
Partners' equity	26,678				26,819				26,678	26,819	12,356
Rental revenue									3,634	4,498	4,432
Net income									473	1,878	2,443
Atlantic-EPR II [Member]
Rental properties, net	20,576				21,037				20,576	21,037	21,498
Cash	131				131				131	131	139
Long-term debt	12,224				12,599				12,224	12,599	12,950
Note payable to EPR	117				117				117	117	117
Partners' equity	8,094				8,202				8,094	8,202	8,317
Rental revenue									2,889	2,889	2,876
Net income									$ 1,401	$ 1,366	$ 1,331