Subsequent Events (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended			0 Months Ended	1 Months Ended
	Mar. 31, 2012	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	Jan. 15, 2012 Repayment of Debt [Member]	Jan. 31, 2012 Issuance of Debt [Member]	Feb. 29, 2012 Repurchase of Equity [Member]	Feb. 29, 2012 Series 6 [Member]	Feb. 16, 2012 Series 6 [Member]
Subsequent Event [Line Items]
Repayments of Unsecured Debt													$ 192,400,000
Debt Instrument, Interest Rate Terms													.0675
Proceeds from Sale of Real Estate										66,000,000	34,900,000	73,000,000
Debt Instrument, Increase, Additional Borrowings														150,000,000
Schedule of Debt [Table Text Block]														$250 million Term Loan
Other Noncash Income (Expense)	7,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date															3.75%
Net Income (Loss) Available to Common Stockholders, Basic	$ 842,000	$ 8,139,000	$ 8,510,000	$ 12,861,000	$ 2,185,000	$ (37,900,000)	$ 7,894,000	$ 7,748,000	$ 11,399,000
Stock Issued During Period, Shares, New Issues																10
Distributions Paid To Preferred Unit Holders										7.45%						6.625%
Preferred Stock, Liquidation Preference Per Share		$ 275,000,000				$ 275,000,000				$ 275,000,000	$ 275,000,000						$ 25