Cover page. Entities [Table] Entities [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Common Shares Of Beneficial Interest Common Shares Of Beneficial Interest [Member] Common Shares Of Beneficial Interest [Member] Depository Shares Depository Shares [Member] Depository Shares [Member] Entity Information [Line Items] Entity Information [Line Items] Entity Address, Address Line One Entity Address, Address Line One Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Emerging Growth Company Entity Emerging Growth Company Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Title of 12(b) Security Title of 12(b) Security Pre-commencement Tender Offer Pre-commencement Tender Offer Soliciting Material Soliciting Material Written Communications Written Communications Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Document Type Document Type Entity Central Index Key Entity Central Index Key Amendment Flag Amendment Flag Document Period End Date Document Period End Date Entity Registrant Name Entity Registrant Name Entity File Number Entity File Number Entity Tax Identification Number Entity Tax Identification Number City Area Code City Area Code Local Phone Number Local Phone Number Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name