Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012 sqft	Sep. 30, 2011 sqft	Sep. 30, 2012 sqft	Sep. 30, 2011 sqft	Dec. 31, 2011 Office property	Sep. 30, 2012 CBD Office property sqft	Sep. 30, 2011 CBD Office sqft	Sep. 30, 2012 CBD Office property sqft	Sep. 30, 2011 CBD Office sqft	Sep. 30, 2012 Suburban Office sqft property	Sep. 30, 2011 Suburban Office sqft	Sep. 30, 2012 Suburban Office sqft property	Sep. 30, 2011 Suburban Office sqft	Sep. 30, 2012 Industrial and Other sqft property	Sep. 30, 2011 Industrial and Other sqft	Sep. 30, 2012 Industrial and Other sqft property	Sep. 30, 2011 Industrial and Other sqft	Dec. 31, 2011 Industrial property	Sep. 30, 2012 Metro Chicago, IL sqft	Sep. 30, 2011 Metro Chicago, IL sqft	Sep. 30, 2012 Metro Chicago, IL sqft	Sep. 30, 2011 Metro Chicago, IL sqft	Sep. 30, 2012 Metro Chicago, IL CBD Office sqft	Sep. 30, 2011 Metro Chicago, IL CBD Office sqft	Sep. 30, 2012 Metro Chicago, IL CBD Office sqft	Sep. 30, 2011 Metro Chicago, IL CBD Office sqft	Sep. 30, 2012 Metro Chicago, IL Suburban Office sqft	Sep. 30, 2011 Metro Chicago, IL Suburban Office sqft	Sep. 30, 2012 Metro Chicago, IL Suburban Office sqft	Sep. 30, 2011 Metro Chicago, IL Suburban Office sqft	Sep. 30, 2012 Metro Chicago, IL Industrial and Other sqft	Sep. 30, 2011 Metro Chicago, IL Industrial and Other sqft	Sep. 30, 2012 Metro Chicago, IL Industrial and Other sqft	Sep. 30, 2011 Metro Chicago, IL Industrial and Other sqft	Sep. 30, 2012 Metro Philadelphia, PA sqft	Sep. 30, 2011 Metro Philadelphia, PA sqft	Sep. 30, 2012 Metro Philadelphia, PA sqft	Sep. 30, 2011 Metro Philadelphia, PA sqft	Sep. 30, 2012 Metro Philadelphia, PA CBD Office sqft	Sep. 30, 2011 Metro Philadelphia, PA CBD Office sqft	Sep. 30, 2012 Metro Philadelphia, PA CBD Office sqft	Sep. 30, 2011 Metro Philadelphia, PA CBD Office sqft	Sep. 30, 2012 Metro Philadelphia, PA Suburban Office sqft	Sep. 30, 2011 Metro Philadelphia, PA Suburban Office sqft	Sep. 30, 2012 Metro Philadelphia, PA Suburban Office sqft	Sep. 30, 2011 Metro Philadelphia, PA Suburban Office sqft	Sep. 30, 2012 Oahu, HI sqft	Sep. 30, 2011 Oahu, HI sqft	Sep. 30, 2012 Oahu, HI sqft	Sep. 30, 2011 Oahu, HI sqft	Sep. 30, 2012 Oahu, HI Industrial and Other sqft	Sep. 30, 2011 Oahu, HI Industrial and Other sqft	Sep. 30, 2012 Oahu, HI Industrial and Other sqft	Sep. 30, 2011 Oahu, HI Industrial and Other sqft	Sep. 30, 2012 Metro Denver, CO sqft	Sep. 30, 2011 Metro Denver, CO sqft	Sep. 30, 2012 Metro Denver, CO sqft	Sep. 30, 2011 Metro Denver, CO sqft	Sep. 30, 2012 Metro Denver, CO CBD Office sqft	Sep. 30, 2011 Metro Denver, CO CBD Office sqft	Sep. 30, 2012 Metro Denver, CO CBD Office sqft	Sep. 30, 2011 Metro Denver, CO CBD Office sqft	Sep. 30, 2012 Metro Denver, CO Suburban Office sqft	Sep. 30, 2011 Metro Denver, CO Suburban Office sqft	Sep. 30, 2012 Metro Denver, CO Suburban Office sqft	Sep. 30, 2011 Metro Denver, CO Suburban Office sqft	Sep. 30, 2012 Metro Denver, CO Industrial and Other sqft	Sep. 30, 2011 Metro Denver, CO Industrial and Other sqft	Sep. 30, 2012 Metro Denver, CO Industrial and Other sqft	Sep. 30, 2011 Metro Denver, CO Industrial and Other sqft	Sep. 30, 2012 Metro Washington, DC sqft	Sep. 30, 2011 Metro Washington, DC sqft	Sep. 30, 2012 Metro Washington, DC sqft	Sep. 30, 2011 Metro Washington, DC sqft	Sep. 30, 2012 Metro Washington, DC CBD Office sqft	Sep. 30, 2011 Metro Washington, DC CBD Office sqft	Sep. 30, 2012 Metro Washington, DC CBD Office sqft	Sep. 30, 2011 Metro Washington, DC CBD Office sqft	Sep. 30, 2012 Metro Washington, DC Suburban Office sqft	Sep. 30, 2011 Metro Washington, DC Suburban Office sqft	Sep. 30, 2012 Metro Washington, DC Suburban Office sqft	Sep. 30, 2011 Metro Washington, DC Suburban Office sqft	Sep. 30, 2012 Other Markets sqft	Sep. 30, 2011 Other Markets sqft	Sep. 30, 2012 Other Markets sqft	Sep. 30, 2011 Other Markets sqft	Sep. 30, 2012 Other Markets CBD Office sqft	Sep. 30, 2011 Other Markets CBD Office sqft	Sep. 30, 2012 Other Markets CBD Office sqft	Sep. 30, 2011 Other Markets CBD Office sqft	Sep. 30, 2012 Other Markets Suburban Office sqft	Sep. 30, 2011 Other Markets Suburban Office sqft	Sep. 30, 2012 Other Markets Suburban Office sqft	Sep. 30, 2011 Other Markets Suburban Office sqft	Sep. 30, 2012 Other Markets Industrial and Other sqft	Sep. 30, 2011 Other Markets Industrial and Other sqft	Sep. 30, 2012 Other Markets Industrial and Other sqft	Sep. 30, 2011 Other Markets Industrial and Other sqft
Segment information
Properties owned						50		50		275		275		201		201
Geographic segments, immediately preceding period			6 months
Geographic segments, minimum percentage of total square feet, annualized revenues or property net operating income, or net operating income defined as rental income less operating expenses			5.00%
Number of properties reclassified to continued operations					7													20
Property square feet	76,832,000	72,287,000	76,832,000	72,287,000		20,360,000	17,820,000	20,360,000	17,820,000	22,683,000	22,147,000	22,683,000	22,147,000	33,789,000	32,320,000	33,789,000	32,320,000		4,868,000	3,850,000	4,868,000	3,850,000	3,600,000	2,582,000	3,600,000	2,582,000	1,164,000	1,164,000	1,164,000	1,164,000	104,000	104,000	104,000	104,000	5,058,000	5,053,000	5,058,000	5,053,000	4,596,000	4,591,000	4,596,000	4,591,000	462,000	462,000	462,000	462,000	17,844,000	17,896,000	17,844,000	17,896,000	17,844,000	17,896,000	17,844,000	17,896,000	2,154,000	2,014,000	2,154,000	2,014,000	672,000	672,000	672,000	672,000	929,000	789,000	929,000	789,000	553,000	553,000	553,000	553,000	1,638,000	1,644,000	1,638,000	1,644,000	428,000	428,000	428,000	428,000	1,210,000	1,216,000	1,210,000	1,216,000	45,270,000	41,830,000	45,270,000	41,830,000	11,064,000	9,547,000	11,064,000	9,547,000	18,918,000	18,516,000	18,918,000	18,516,000	15,288,000	13,767,000	15,288,000	13,767,000
Property rental income	$ 261,661	$ 241,785	$ 768,281	$ 670,396		$ 127,459	$ 106,090	$ 374,941	$ 278,098	$ 91,743	$ 94,513	$ 269,010	$ 271,264	$ 42,459	$ 41,182	$ 124,330	$ 121,034		$ 34,016	$ 21,403	$ 97,896	$ 40,792	$ 26,900	$ 14,510	$ 77,947	$ 18,736	$ 7,005	$ 6,783	$ 19,616	$ 21,710	$ 111	$ 110	$ 333	$ 346	$ 30,207	$ 30,741	$ 91,104	$ 90,230	$ 29,134	$ 29,363	$ 87,721	$ 86,273	$ 1,073	$ 1,378	$ 3,383	$ 3,957	$ 18,318	$ 18,238	$ 56,511	$ 54,951	$ 18,318	$ 18,238	$ 56,511	$ 54,951	$ 10,889	$ 11,327	$ 32,187	$ 33,668	$ 4,800	$ 4,998	$ 15,169	$ 16,040	$ 3,685	$ 4,005	$ 10,162	$ 10,954	$ 2,404	$ 2,324	$ 6,856	$ 6,674	$ 9,172	$ 13,567	$ 30,467	$ 32,688	$ 3,073	$ 4,756	$ 10,738	$ 11,596	$ 6,099	$ 8,811	$ 19,729	$ 21,092	$ 159,059	$ 146,509	$ 460,116	$ 418,067	$ 63,552	$ 52,463	$ 183,366	$ 145,453	$ 73,881	$ 73,536	$ 216,120	$ 213,551	$ 21,626	$ 20,510	$ 60,630	$ 59,063
Property net operating income	$ 149,084	$ 137,102	$ 443,521	$ 384,693		$ 67,228	$ 56,677	$ 201,427	$ 149,531	$ 51,482	$ 52,292	$ 152,327	$ 152,576	$ 30,374	$ 28,133	$ 89,767	$ 82,586		$ 18,815	$ 11,831	$ 51,932	$ 23,329	$ 14,858	$ 8,044	$ 41,145	$ 10,225	$ 3,854	$ 3,683	$ 10,477	$ 12,787	$ 103	$ 104	$ 310	$ 317	$ 14,945	$ 15,101	$ 46,953	$ 44,303	$ 14,829	$ 14,854	$ 46,606	$ 43,919	$ 116	$ 247	$ 347	$ 384	$ 14,294	$ 13,637	$ 43,979	$ 40,883	$ 14,294	$ 13,637	$ 43,979	$ 40,883	$ 6,995	$ 7,413	$ 21,849	$ 22,766	$ 3,022	$ 3,136	$ 9,851	$ 10,455	$ 2,746	$ 3,086	$ 8,075	$ 8,640	$ 1,227	$ 1,191	$ 3,923	$ 3,671	$ 5,689	$ 9,899	$ 19,990	$ 22,247	$ 2,370	$ 3,942	$ 7,962	$ 8,869	$ 3,319	$ 5,957	$ 12,028	$ 13,378	$ 88,346	$ 79,221	$ 258,818	$ 231,165	$ 32,149	$ 26,701	$ 95,863	$ 76,063	$ 41,447	$ 39,319	$ 121,400	$ 117,387	$ 14,750	$ 13,201	$ 41,555	$ 37,715