Grants to Trustees (Details) (Individual Trustee Grant Agreements [Member], USD $)	0 Months Ended
	Jun. 25, 2012	May 22, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of independent trustees (in trustees)	2	4
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock granted to trustees (in shares)	915	6,000
Stock granted to trustees, vested in period (in shares)		1,500
Stock granted to trustees, weighted-average grant date fair value (in dollars per share)	$ 13.39	$ 13.03