Unconsolidated Real Estate Joint Ventures (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended				12 Months Ended		9 Months Ended		12 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Atlantic-EPR I [Member]	Sep. 30, 2011 Atlantic-EPR I [Member]	Dec. 31, 2011 Atlantic-EPR I [Member]	Jan. 02, 2012 Atlantic-EPR I [Member]	Sep. 30, 2012 Atlantic-EPR II [Member]	Sep. 30, 2011 Atlantic-EPR II [Member]	Dec. 31, 2011 Atlantic-EPR II [Member]	Sep. 30, 2012 Atlantic-EPR I and II [Member] jointventures	Sep. 30, 2012 Theatre Project China [Member] properties	Sep. 30, 2011 Theatre Project China [Member]	Dec. 31, 2011 Theatre Project China [Member] properties
Investment interest in unconsolidated real estate joint ventures					42.10%				29.60%
Number of unconsolidated joint ventures (in joint ventures)												2	3		3
Investment in joint ventures								$ 14,900,000					$ 4,500,000		$ 4,200,000
Conversion of equity to mortgage loan related to atlantic-EPR I			14,852,000	0	14,900,000
Income from investments in unconsolidated real estate joint venture	342,000	676,000	666,000	2,231,000	45,000	1,900,000			326,000	279,000				54,000
Distributions from joint ventures			827,000	2,176,000	473,000	1,900,000			355,000	310,000
Maximum exchange of ownership interest per year			10.00%
Additional amount contributed in equity					1,300,000		2,500,000		490,000		258,000
Additional ownership interest in unconsolidated real estate joint ventures					6.00%		11.30%		3.80%		2.00%
Loss from investments in unconsolidated real estate joint venture													$ 295,000