Noncontrolling Interests (Redeemable Preferred Units) (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Feb. 15, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two Preferred Units	1,030,748
Series Two Preferred Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Units converted	82,296
Series Two Preferred Units [Member] | Noncontrolling Interests [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Series Two Preferred Units	1,030,748
Liquidation preference percentage	6.00%
Preferred Units liquidation preference	$ 50.00
Operating Units liquidation preference	$ 38.10
OP Units for each Preferred Unit	1.312336
Distributions to Series Two Preferred Units		$ 0.75616
Number of holders exercising redemption rights	0		0	0	0
OP Units [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Units converted	108,000
Redemption Year Two Thousand Thirteen [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Maximum redeemable Preferred Units	1,007,662
Dates Series Two Preferred holders can require Operating Partnership to redeem their units for cash	May 14, 2013
Series Two Preferred Units redemption price per unit	$ 50.00
Maximum portion that may be required for redemption of total	0.166666666667
Redemption Year Two Thousand Fourteen [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Maximum redeemable Preferred Units	1,007,662
Dates Series Two Preferred holders can require Operating Partnership to redeem their units for cash	May 12, 2014
Series Two Preferred Units redemption price per unit	$ 50.00
Maximum portion that may be required for redemption of total	0.166666666667