Debt Of The Operating Partnership (Mortgage Loans) (Details)						3 Months Ended		12 Months Ended			3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended		3 Months Ended				3 Months Ended		3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended						3 Months Ended
	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Mar. 31, 2012 Mortgage Loans [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] USD ($)	Mar. 31, 2012 Mortgage Loans [Member] Secured Term Debt [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Secured Term Debt [Member]	Dec. 31, 2011 Mortgage Loans [Member] Secured Term Debt [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 200 Paul Avenue 1-4 [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 200 Paul Avenue 1-4 [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Mundells Roundabout [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] Mundells Roundabout [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 2045 & 2055 LaFayette Street [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 2045 & 2055 LaFayette Street [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 34551 Ardenwood Boulevard 1-4 [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 34551 Ardenwood Boulevard 1-4 [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 1100 Space Park Drive [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 1100 Space Park Drive [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 1350 Duane Avenue/3080 Raymond Street [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 1350 Duane Avenue/3080 Raymond Street [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 600 West Seventh Street [Member] USD ($)	Dec. 31, 2011 Mortgage Loans [Member] 600 West Seventh Street [Member] USD ($)	Mar. 31, 2012 Mortgage Loans [Member] 150 South First Street [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 150 South First Street [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 360 Spear Street [Member] USD ($)	Dec. 31, 2011 Mortgage Loans [Member] 360 Spear Street [Member] USD ($)	Mar. 31, 2012 Mortgage Loans [Member] 114 Rue Ambroise Croizat [Member]		Dec. 31, 2011 Mortgage Loans [Member] 114 Rue Ambroise Croizat [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 2334 Lundy Place [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 2334 Lundy Place [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Clonshaugh Industrial Estate II [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] Clonshaugh Industrial Estate II [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 1500 Space Park Drive [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 1500 Space Park Drive [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Unit 9, Blanchardstown Corporate Park [Member]		Dec. 31, 2011 Mortgage Loans [Member] Unit 9, Blanchardstown Corporate Park [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Cressex 1 [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] Cressex 1 [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 1201 Comstock Street [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 1201 Comstock Street [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Paul van Vlissingenstraat 16 [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] Paul van Vlissingenstraat 16 [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 800 Central Expressway [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] 800 Central Expressway [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Chemin de l'Epinglier 2 [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] Chemin de l'Epinglier 2 [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Gyroscoopweg 2E-2F [Member] USD ($)		Dec. 31, 2011 Mortgage Loans [Member] Gyroscoopweg 2E-2F [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Manchester Technopark [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] Manchester Technopark [Member] GBP (£)		Dec. 31, 2011 Mortgage Loans [Member] Manchester Technopark [Member] USD ($)		Mar. 31, 2012 Mortgage Loans [Member] 731 East Trade Street [Member] USD ($)	Dec. 31, 2011 Mortgage Loans [Member] 731 East Trade Street [Member] USD ($)	Mar. 31, 2012 EUR [Member]	Dec. 31, 2011 EUR [Member]	Mar. 31, 2012 EUR [Member] Mortgage Loans [Member]	Dec. 31, 2010 EUR [Member] Mortgage Loans [Member]	Mar. 31, 2012 GBP [Member]	Dec. 31, 2011 GBP [Member]	Mar. 31, 2012 GBP [Member] Mortgage Loans [Member]	Dec. 31, 2010 GBP [Member] Mortgage Loans [Member]
Debt of the Operating Partnership [Line Items]
Interest rate	4.125%					5.65%	[1],[2]				5.74%	[1]							5.93%	[1]			5.95%	[1]			5.89%	[1]			5.42%	[1]			5.80%		6.30%	[1]			6.32%						5.96%	[1]							6.15%	[1]							5.68%	[3]																							5.68%	[3]	5.68%	[3]			8.22%
Variable Rate Basis															3-month GBP LIBOR + 1.20%	[4]																											3-month EURIBOR + 1.35%	[4]							3-month EURIBOR + 4.50%	[4],[5]							3-month EURIBOR + 1.35%	[4]							1-month LIBOR + 3.50%	[4],[5],[6]			3-month EURIBOR + 1.60%	[4]			1-month LIBOR + 4.75%	[4],[6],[7]			3-month EURIBOR + 1.50%	[4],[5]			3-month EURIBOR + 1.50%	[4],[5],[6]
Maturity Date						Nov. 11, 2014	[1],[2]				Oct. 08, 2015	[1]			Nov. 30, 2013				Feb. 06, 2017	[1]			Nov. 11, 2016	[1]			Dec. 11, 2016	[1]			Oct. 01, 2012	[1]			Mar. 15, 2016		Feb. 06, 2017	[1]			Nov. 08, 2013		Jan. 18, 2012	[8]			Nov. 11, 2016	[1]			Sep. 04, 2014	[9]			Oct. 05, 2013	[1]			Jan. 18, 2012	[8]			Oct. 16, 2014	[3]			Jun. 24, 2012				Jul. 18, 2013				Jun. 09, 2013	[1]			Jul. 18, 2013				Oct. 18, 2013				Oct. 16, 2014	[3]	Oct. 16, 2014	[3]			Jul. 01, 2020
Unamortized net premium	$ 2,072,000		$ 2,072,000	[10]	$ 2,077,000
Mortgage loans, net of premiums	875,075,000	947,132,000	875,075,000	[10]	947,132,000	138,123,000	[1],[2]		138,828,000	[1],[2]	74,009,000	[1]	74,458,000	[1]	68,554,000	[11]	66,563,000	[11]	65,318,000	[1]	65,551,000	[1]	53,449,000	[1]	53,627,000	[1]	53,429,000	[1]	53,609,000	[1]	52,800,000	[1]	52,800,000	[1]	52,334,000	52,709,000	51,339,000	[1]	51,508,000	[1]	47,331,000	47,569,000			39,483,000	[12]	38,873,000	[1]	39,003,000	[1]	40,029,000	[9]	38,883,000	[12],[9]	37,337,000	[1]	37,875,000	[1]			33,946,000	[12]	28,494,000	[3]	27,786,000	[11],[3]	15,952,000	[1],[9]	16,163,000	[1],[9]	13,655,000	[12]	13,319,000	[12]	10,000,000	[1]	10,000,000	[1]	9,880,000	[12]	9,636,000	[12]	8,695,000	[12]	8,480,000	[12]	8,668,000	[11],[3]			8,453,000	[11],[3]	4,734,000	4,806,000
Mortgage loans on real estate, number								6
Exchange rate																																																																																															1.33	1.30	1.33	1.30	1.60	1.55	1.60	1.55
Letter of credit security amount																																																																																									£ 7,800,000

[1] The respective borrower's assets and credit are not available to satisfy the debts and other obligations of affiliates or any other person.

[2] This amount represents six mortgage loans secured by our interests in 36 NE 2nd Street, 3300 East Birch Street, 100 & 200 Quannapowitt Parkway, 300 Boulevard East, 4849 Alpha Road, and 11830 Webb Chapel Road. Each of these loans is cross-collateralized by the six properties.

[3] These loans are also secured by a £7.8 million letter of credit. These loans are cross-collateralized by the two properties.

[4] We have entered into interest rate swap or interest rate cap agreements as a cash flow hedge for interest generated by these US LIBOR, EURIBOR and GBP LIBOR based loans. See note [13] for further information.

[5] The Operating Partnership or its subsidiary provides a limited recourse guarantee with respect to this loan.

[6] The respective borrower’s assets and credit are not available to satisfy the debts and other obligations of affiliates or any other person.

[7] These loans are also secured by a £7.8 million letter of credit. These loans are cross-collateralized by the two properties.

[8] These mortgage loans were repaid in full in January 2012.

[9] The Operating Partnership or its subsidiary provides a limited recourse guarantee with respect to this loan.

[10] Our mortgage loans are generally non-recourse to us, subject to carve outs for specified actions by us or specified undisclosed environmental liabilities. As of March 31, 2012, we had provided limited recourse guarantees with respect to approximately $56.0 million principal amount of the outstanding mortgage indebtedness, and partial letter of credit support with respect to approximately an additional $37.2 million of the outstanding mortgage indebtedness.

[11] Based on exchange rate of $1.60 to £1.00 as of March 31, 2012 and $1.55 to £1.00 as of December 31, 2011.

[12] Based on exchange rate of $1.33 to €1.00 as of March 31, 2012 and $1.30 to €1.00 as of December 31, 2011.