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Repayment Of Debt With Capital Contributions.

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Investments In Unconsolidated Joint Ventures (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended													0 Months Ended		3 Months Ended		0 Months Ended
	Nov. 04, 2011	Nov. 03, 2011	Jun. 28, 2011 Operating Partnership [Member] Mountain View Research Park [Member]	Jun. 28, 2011 Operating Partnership [Member] Mountain View Research Park [Member] Advanced To Date [Member]	Mar. 16, 2011 Mountain View Technology Park [Member]	Mar. 16, 2011 Mountain View Technology Park [Member] Previous Maturity Date [Member]	Jun. 28, 2011 Mountain View Technology Park [Member] Original Maturity Date [Member]	Jun. 28, 2011 Mountain View Technology Park [Member] Extended Maturity Date [Member]	Jun. 28, 2011 Mountain View Research Park [Member]	Jun. 28, 2011 Mountain View Research Park [Member] Previous Mortgage Loan [Member]	Jun. 28, 2011 Mountain View Research Park [Member] New Mortgage Loan [Member]	Jan. 18, 2011 Five Hundred North Capitol Street, NW [Member]	Mar. 26, 2011 Five Hundred North Capitol Street, NW [Member]	Jun. 03, 2011 Annapolis Junction [Member]	Mar. 31, 2011 Annapolis Junction [Member]	Mar. 31, 2011 Annapolis Junction [Member] Previous Mortgage Loan [Member]	Mar. 31, 2011 Annapolis Junction [Member] New Mortgage Loan [Member]	Aug. 12, 2011 Two Grand Central Tower [Member]
Schedule of Equity Method Investments [Line Items]
Mortgage loan extension of maturity date (months)																	36
Initial mortgage loan extension of maturity date (months)					2
Description of variable rate basis					LIBOR plus 1.50% per annum					LIBOR plus 1.75% per annum	LIBOR plus 2.50% per annum					LIBOR plus 1.00% per annum	LIBOR plus 1.75% per annum
Basis spread on variable rate basis					1.50%					1.75%	2.50%					1.00%	1.75%
Interest at a fixed rate	2.875%	3.70%	10.00%
Maturity date	Feb. 15, 2037	Nov. 15, 2018				May 31, 2011	Mar. 31, 2011	Nov. 15, 2011		May 31, 2011	May 31, 2014					Sep. 12, 2011	Mar. 31, 2018
Square footage of signed lease												171,000
Ownership percentage													30.00%	50.00%	50.00%			60.00%
Carrying amount of loan					$ 24.7					$ 112.3	$ 92.0					$ 42.7	$ 42.3	$ 176.6
Square footage of real estate property														120,000				650,000
Number of extension options																	1
Mortgage loan extension option (years)																	3
Repayment of previous mortgage by investor									20.3
Contractual sale price																		401.0
Loan to value-added fund			12.0	6.4
Impairment of long-lived assets to be disposed of																		39.4
Carrying value of net assets of property sold																		$ 425.7