Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012 sqft	Jun. 30, 2011 sqft	Jun. 30, 2012 sqft	Jun. 30, 2011 sqft	Dec. 31, 2011 Office property	Sep. 30, 2011 Office property	Jun. 30, 2012 CBD Office sqft property	Jun. 30, 2011 CBD Office sqft	Jun. 30, 2012 CBD Office sqft property	Jun. 30, 2011 CBD Office sqft	Jun. 30, 2012 Suburban Office sqft property	Jun. 30, 2011 Suburban Office sqft	Jun. 30, 2012 Suburban Office sqft property	Jun. 30, 2011 Suburban Office sqft	Jun. 30, 2012 Industrial and Other property sqft	Jun. 30, 2011 Industrial and Other sqft	Jun. 30, 2012 Industrial and Other property sqft	Jun. 30, 2011 Industrial and Other sqft	Dec. 31, 2011 Industrial property	Sep. 30, 2011 Industrial property	Jun. 30, 2012 Metro Chicago, IL sqft	Jun. 30, 2011 Metro Chicago, IL sqft	Jun. 30, 2012 Metro Chicago, IL sqft	Jun. 30, 2011 Metro Chicago, IL sqft	Jun. 30, 2012 Metro Chicago, IL CBD Office sqft	Jun. 30, 2011 Metro Chicago, IL CBD Office sqft	Jun. 30, 2012 Metro Chicago, IL CBD Office sqft	Jun. 30, 2011 Metro Chicago, IL CBD Office sqft	Jun. 30, 2012 Metro Chicago, IL Suburban Office sqft	Jun. 30, 2011 Metro Chicago, IL Suburban Office sqft	Jun. 30, 2012 Metro Chicago, IL Suburban Office sqft	Jun. 30, 2011 Metro Chicago, IL Suburban Office sqft	Jun. 30, 2012 Metro Chicago, IL Industrial and Other sqft	Jun. 30, 2011 Metro Chicago, IL Industrial and Other sqft	Jun. 30, 2012 Metro Chicago, IL Industrial and Other sqft	Jun. 30, 2011 Metro Chicago, IL Industrial and Other sqft	Jun. 30, 2012 Metro Philadelphia, PA sqft	Jun. 30, 2011 Metro Philadelphia, PA sqft	Jun. 30, 2012 Metro Philadelphia, PA sqft	Jun. 30, 2011 Metro Philadelphia, PA sqft	Jun. 30, 2012 Metro Philadelphia, PA CBD Office sqft	Jun. 30, 2011 Metro Philadelphia, PA CBD Office sqft	Jun. 30, 2012 Metro Philadelphia, PA CBD Office sqft	Jun. 30, 2011 Metro Philadelphia, PA CBD Office sqft	Jun. 30, 2012 Metro Philadelphia, PA Suburban Office sqft	Jun. 30, 2011 Metro Philadelphia, PA Suburban Office sqft	Jun. 30, 2012 Metro Philadelphia, PA Suburban Office sqft	Jun. 30, 2011 Metro Philadelphia, PA Suburban Office sqft	Jun. 30, 2012 Oahu, HI sqft	Jun. 30, 2011 Oahu, HI sqft	Jun. 30, 2012 Oahu, HI sqft	Jun. 30, 2011 Oahu, HI sqft	Jun. 30, 2012 Oahu, HI Industrial and Other sqft	Jun. 30, 2011 Oahu, HI Industrial and Other sqft	Jun. 30, 2012 Oahu, HI Industrial and Other sqft	Jun. 30, 2011 Oahu, HI Industrial and Other sqft	Jun. 30, 2012 Metro Denver, CO sqft	Jun. 30, 2011 Metro Denver, CO sqft	Jun. 30, 2012 Metro Denver, CO sqft	Jun. 30, 2011 Metro Denver, CO sqft	Jun. 30, 2012 Metro Denver, CO CBD Office sqft	Jun. 30, 2011 Metro Denver, CO CBD Office sqft	Jun. 30, 2012 Metro Denver, CO CBD Office sqft	Jun. 30, 2011 Metro Denver, CO CBD Office sqft	Jun. 30, 2012 Metro Denver, CO Suburban Office sqft	Jun. 30, 2011 Metro Denver, CO Suburban Office sqft	Jun. 30, 2012 Metro Denver, CO Suburban Office sqft	Jun. 30, 2011 Metro Denver, CO Suburban Office sqft	Jun. 30, 2012 Metro Denver, CO Industrial and Other sqft	Jun. 30, 2011 Metro Denver, CO Industrial and Other sqft	Jun. 30, 2012 Metro Denver, CO Industrial and Other sqft	Jun. 30, 2011 Metro Denver, CO Industrial and Other sqft	Jun. 30, 2012 Metro Washington, DC sqft	Jun. 30, 2011 Metro Washington, DC sqft	Jun. 30, 2012 Metro Washington, DC sqft	Jun. 30, 2011 Metro Washington, DC sqft	Jun. 30, 2012 Metro Washington, DC CBD Office sqft	Jun. 30, 2011 Metro Washington, DC CBD Office sqft	Jun. 30, 2012 Metro Washington, DC CBD Office sqft	Jun. 30, 2011 Metro Washington, DC CBD Office sqft	Jun. 30, 2012 Metro Washington, DC Suburban Office sqft	Jun. 30, 2011 Metro Washington, DC Suburban Office sqft	Jun. 30, 2012 Metro Washington, DC Suburban Office sqft	Jun. 30, 2011 Metro Washington, DC Suburban Office sqft	Jun. 30, 2012 Other Markets sqft	Jun. 30, 2011 Other Markets sqft	Jun. 30, 2012 Other Markets sqft	Jun. 30, 2011 Other Markets sqft	Jun. 30, 2012 Other Markets CBD Office sqft	Jun. 30, 2011 Other Markets CBD Office sqft	Jun. 30, 2012 Other Markets CBD Office sqft	Jun. 30, 2011 Other Markets CBD Office sqft	Jun. 30, 2012 Other Markets Suburban Office sqft	Jun. 30, 2011 Other Markets Suburban Office sqft	Jun. 30, 2012 Other Markets Suburban Office sqft	Jun. 30, 2011 Other Markets Suburban Office sqft	Jun. 30, 2012 Other Markets Industrial and Other sqft	Jun. 30, 2011 Other Markets Industrial and Other sqft	Jun. 30, 2012 Other Markets Industrial and Other sqft	Jun. 30, 2011 Other Markets Industrial and Other sqft
Segment information
Properties owned							48		48		272		272		199		199
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 discontinued operations						12														1
Number of properties reclassified to continued operations					7														20
Property square feet	74,753,000	69,044,000	74,753,000	69,044,000			19,874,000	14,544,000	19,874,000	14,544,000	22,602,000	22,165,000	22,602,000	22,165,000	32,277,000	32,335,000	32,277,000	32,335,000			4,860,000	2,339,000	4,860,000	2,339,000	3,592,000	1,072,000	3,592,000	1,072,000	1,164,000	1,164,000	1,164,000	1,164,000	104,000	103,000	104,000	103,000	5,058,000	5,054,000	5,058,000	5,054,000	4,596,000	4,592,000	4,596,000	4,592,000	462,000	462,000	462,000	462,000	17,876,000	17,914,000	17,876,000	17,914,000	17,876,000	17,914,000	17,876,000	17,914,000	2,014,000	2,014,000	2,014,000	2,014,000	672,000	672,000	672,000	672,000	789,000	789,000	789,000	789,000	553,000	553,000	553,000	553,000	1,649,000	1,644,000	1,649,000	1,644,000	428,000	428,000	428,000	428,000	1,221,000	1,216,000	1,221,000	1,216,000	43,296,000	40,079,000	43,296,000	40,079,000	10,586,000	7,780,000	10,586,000	7,780,000	18,966,000	18,534,000	18,966,000	18,534,000	13,744,000	13,765,000	13,744,000	13,765,000
Property rental income	$ 255,374	$ 217,938	$ 506,620	$ 428,611			$ 126,261	$ 90,029	$ 247,482	$ 172,008	$ 88,966	$ 87,932	$ 177,267	$ 176,751	$ 40,147	$ 39,977	$ 81,871	$ 79,852			$ 33,331	$ 11,470	$ 63,880	$ 19,389	$ 26,472	$ 4,226	$ 51,047	$ 4,226	$ 6,748	$ 7,134	$ 12,611	$ 14,927	$ 111	$ 110	$ 222	$ 236	$ 30,493	$ 29,859	$ 60,897	$ 59,489	$ 29,287	$ 28,637	$ 58,587	$ 56,910	$ 1,206	$ 1,222	$ 2,310	$ 2,579	$ 18,298	$ 18,117	$ 38,193	$ 36,713	$ 18,298	$ 18,117	$ 38,193	$ 36,713	$ 10,055	$ 11,304	$ 21,202	$ 22,341	$ 4,815	$ 5,679	$ 10,369	$ 11,042	$ 2,883	$ 3,459	$ 6,381	$ 6,949	$ 2,357	$ 2,166	$ 4,452	$ 4,350	$ 10,409	$ 9,740	$ 21,295	$ 19,121	$ 3,646	$ 3,384	$ 7,665	$ 6,840	$ 6,763	$ 6,356	$ 13,630	$ 12,281	$ 152,788	$ 137,448	$ 301,153	$ 271,558	$ 62,041	$ 48,103	$ 119,814	$ 92,990	$ 71,366	$ 69,761	$ 142,335	$ 140,015	$ 19,381	$ 19,584	$ 39,004	$ 38,553
Property net operating income (loss)	$ 147,281	$ 127,315	$ 294,437	$ 247,591			$ 67,262	$ 48,404	$ 134,199	$ 92,854	$ 50,328	$ 50,945	$ 100,845	$ 100,284	$ 29,691	$ 27,966	$ 59,393	$ 54,453			$ 17,672	$ 6,699	$ 33,117	$ 11,498	$ 13,909	$ 2,181	$ 26,287	$ 2,181	$ 3,660	$ 4,415	$ 6,623	$ 9,104	$ 103	$ 103	$ 207	$ 213	$ 16,321	$ 14,790	$ 32,008	$ 29,202	$ 16,193	$ 14,809	$ 31,777	$ 29,065	$ 128	$ (19)	$ 231	$ 137	$ 14,171	$ 13,825	$ 29,685	$ 27,246	$ 14,171	$ 13,825	$ 29,685	$ 27,246	$ 6,688	$ 7,877	$ 14,786	$ 15,353	$ 3,066	$ 3,819	$ 6,829	$ 7,319	$ 2,168	$ 2,786	$ 5,261	$ 5,554	$ 1,454	$ 1,272	$ 2,696	$ 2,480	$ 6,625	$ 6,196	$ 14,301	$ 12,348	$ 2,431	$ 2,318	$ 5,592	$ 4,927	$ 4,194	$ 3,878	$ 8,709	$ 7,421	$ 85,804	$ 77,928	$ 170,540	$ 151,944	$ 31,663	$ 25,277	$ 63,714	$ 49,362	$ 40,178	$ 39,885	$ 80,021	$ 78,068	$ 13,963	$ 12,766	$ 26,805	$ 24,514