Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended		3 Months Ended				3 Months Ended			6 Months Ended	12 Months Ended	6 Months Ended		3 Months Ended			6 Months Ended	12 Months Ended	6 Months Ended		3 Months Ended			6 Months Ended	12 Months Ended	6 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2012 Stock Appreciation Rights (SARs) [Member]	Jan. 24, 2012 Stock Appreciation Rights (SARs) [Member]	Jun. 30, 2012 Dividend Reinvestment and Share Purchase Plan [Member]	Mar. 31, 2012 Dividend Reinvestment and Share Purchase Plan [Member]	Sep. 30, 2012 7.75% Series A preferred shares[Member]	Jun. 30, 2012 7.75% Series A preferred shares[Member]	Mar. 31, 2012 7.75% Series A preferred shares[Member]	Jun. 30, 2012 7.75% Series A preferred shares[Member]	Dec. 31, 2011 7.75% Series A preferred shares[Member]	Jun. 30, 2012 7.75% Series A preferred shares[Member] At Market Issuance Sales Agreement [Member]	Jun. 30, 2012 7.75% Series A preferred shares[Member] At Market Issuance Sales Agreement After June Thirty [Member]	Sep. 30, 2012 8.375% Series B preferred shares[Member]	Jun. 30, 2012 8.375% Series B preferred shares[Member]	Mar. 31, 2012 8.375% Series B preferred shares[Member]	Jun. 30, 2012 8.375% Series B preferred shares[Member]	Dec. 31, 2011 8.375% Series B preferred shares[Member]	Jun. 30, 2012 8.375% Series B preferred shares[Member] At Market Issuance Sales Agreement [Member]	Jun. 30, 2012 8.375% Series B preferred shares[Member] At Market Issuance Sales Agreement After June Thirty [Member]	Sep. 30, 2012 8.875% Series C preferred shares[Member]	Jun. 30, 2012 8.875% Series C preferred shares[Member]	Mar. 31, 2012 8.875% Series C preferred shares[Member]	Jun. 30, 2012 8.875% Series C preferred shares[Member]	Dec. 31, 2011 8.875% Series C preferred shares[Member]	Jun. 30, 2012 8.875% Series C preferred shares[Member] At Market Issuance Sales Agreement [Member]	Jun. 30, 2012 8.875% Series C preferred shares[Member] At Market Issuance Sales Agreement After June Thirty [Member]
Class of Stock [Line Items]
Cash dividend per share											$ 0.484375	$ 0.484375	$ 0.484375					$ 0.5234375	$ 0.5234375	$ 0.5234375					$ 0.5546875	$ 0.5546875	$ 0.5546875
Preferred stock, dividend rate, percentage	8.375%										7.75%	7.75%	7.75%	7.75%	7.75%				8.375%	8.375%	8.375%	8.375%			8.875%	8.875%	8.875%	8.875%	8.875%
Preferred shares authorized to be issued under agreement													2,000,000							2,000,000							2,000,000
Preferred share issuance, net of costs incurred					$ 1,147	$ 0
Net proceeds received from issuance of preferred shares																552	159						275	221						465	402
Stock appreciation rights								2,172,000
Stock appreciation rights value based on a Black-Scholes option pricing model							6,091
Registered and reserved common shares										10,500,000
Weighted-average price per shares									$ 5.10
Preferred Shares Total Issued												2,787,931		2,787,931	2,760,000	27,931	8,069		2,271,620		2,271,620	2,258,000	13,320	10,680		1,621,430		1,621,430	1,600,000	21,430	18,570
Cumulative Redeemable Preferred Shares, par value												$ 0.01		$ 0.01	$ 0.01				$ 0.01		$ 0.01	$ 0.01				$ 0.01		$ 0.01	$ 0.01
weighted-average price per shares																$ 20.37	$ 20.30						$ 21.32	$ 21.34						$ 22.39	$ 22.34
Aggregate of Series A,B,C Preferred Shares available for issuance												1,964,000		1,964,000					1,976,000		1,976,000					1,960,000		1,960,000
Equity (Textual) [Abstract]
Dividend on preferred shares		3,406	3,407
Dividend, total			3,992		3,985
Distributions declared per common share		$ 0.08	$ 0.16	$ 0.06	$ 0.16	$ 0.15
Common shares purchased on open market for issuance to non-management trustees, value					210
Common shares purchased on open market for issuance to non-management trustees, shares			36,750
Number of phantom unit awards that redeemed during period					220,823
Common shares pursuant to the DRSPP					1,496,826
Net proceeds received					7,595
Common shares remaining available under the DRSPP		7,790,756			7,790,756
Common shares in an underwritten public offering					6,950,000
Public offering price					$ 5.30
Proceeds received during period from common share issuance in underwritten public offering					$ 34,750