Debt of the Operating Partnership (Mortgage Loans) (Details)														6 Months Ended		12 Months Ended		6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended		6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended			6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended					6 Months Ended					6 Months Ended				6 Months Ended
	Jun. 30, 2011 USD ($)	Dec. 31, 2010 USD ($)	Jun. 30, 2011 Euro [Member]	Dec. 31, 2010 Euro [Member]	Jun. 30, 2011 Euro [Member] Mortgage Loans [Member]	Dec. 31, 2010 Euro [Member] Mortgage Loans [Member]	Jun. 30, 2011 British Sterling [Member]	Dec. 31, 2010 British Sterling [Member]	Jun. 30, 2011 British Sterling [Member] Mortgage Loans [Member]	Dec. 31, 2010 British Sterling [Member] Mortgage Loans [Member]	Jun. 30, 2011 Mortgage Loans [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] USD ($)	Jun. 30, 2011 Mortgage Loans [Member] Secured Term Debt [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Secured Term Debt [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 3 Corporate Place [Member]		Dec. 31, 2010 Mortgage Loans [Member] 3 Corporate Place [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 200 Paul Avenue 1-4 [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 200 Paul Avenue 1-4 [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 2045 & 2055 LaFayette Street [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 2045 & 2055 LaFayette Street [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Mundells Roundabout [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Mundells Roundabout [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 600 West Seventh Street [Member] USD ($)	Dec. 31, 2010 Mortgage Loans [Member] 600 West Seventh Street [Member] USD ($)	Jun. 30, 2011 Mortgage Loans [Member] 34551 Ardenwood Boulevard 1-4 [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 34551 Ardenwood Boulevard 1-4 [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 1100 Space Park Drive [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 1100 Space Park Drive [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 1350 Duane Avenue/3080 Raymond Street [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 1350 Duane Avenue/3080 Raymond Street [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 150 South First Street [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 150 South First Street [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 114 Rue Ambroise Croizat [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 114 Rue Ambroise Croizat [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Clonshaugh Industrial Estate II [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Clonshaugh Industrial Estate II [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 1500 Space Park Drive [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 1500 Space Park Drive [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 2334 Lundy Place [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 2334 Lundy Place [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Unit 9, Blanchardstown Corporate Park [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Unit 9, Blanchardstown Corporate Park [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Cressex 1 [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Cressex 1 [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 6 Braham Street [Member]		Dec. 31, 2010 Mortgage Loans [Member] 6 Braham Street [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 1201 Comstock Street [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 1201 Comstock Street [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Datacenter Park Dallas [Member]		Dec. 31, 2010 Mortgage Loans [Member] Datacenter Park Dallas [Member] USD ($)	Jun. 30, 2011 Mortgage Loans [Member] Paul van Vlissingenstraat 16 [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Paul van Vlissingenstraat 16 [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Chemin de l'Epinglier 2 [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Chemin de l'Epinglier 2 [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 800 Central Expressway [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] 800 Central Expressway [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Gyroscoopweg 2E-2F [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Gyroscoopweg 2E-2F [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Gyroscoopweg 2E-2F [Member] EUR (€)	Jun. 30, 2011 Mortgage Loans [Member] 1125 Energy Park Drive [Member] USD ($)		Mar. 01, 2012 Mortgage Loans [Member] 1125 Energy Park Drive [Member]	Dec. 31, 2010 Mortgage Loans [Member] 1125 Energy Park Drive [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] Manchester Technopark [Member] USD ($)		Dec. 31, 2010 Mortgage Loans [Member] Manchester Technopark [Member] USD ($)		Jun. 30, 2011 Mortgage Loans [Member] 731 East Trade Street [Member] USD ($)	Dec. 31, 2010 Mortgage Loans [Member] 731 East Trade Street [Member] USD ($)
Interest Rate at June 30, 2011														5.65%	[1],[2]			6.72%	[1],[3]			5.74%	[1]			5.93%	[1]							5.80%		5.95%	[1]			5.89%	[1]			5.42%	[1]			6.30%	[1]											6.15%	[1]			5.96%	[1]							5.68%	[4]											5.00%																				7.62%	[5]	9.62%			5.68%	[4]			8.22%
Variable Rate Basis																														3-month GBP LIBOR + 1.20%	[6]																					3-month EURIBOR + 1.35%	[6]			3-month EURIBOR + 4.50%	[6]											3-month EURIBOR + 1.35%	[6]							3-month GBP LIBOR + 0.90%	[6]			1-month LIBOR + 3.50%	[6]						3-month EURIBOR + 1.60%	[6]			3-month EURIBOR + 1.50%	[6]			1-month LIBOR + 4.75%	[6]			3-month EURIBOR + 1.50%	[6]
Maturity Date														Nov. 11, 2014	[1],[2]			Aug. 01, 2011	[7]			Oct. 08, 2015	[1]			Feb. 06, 2017	[1]			Nov. 30, 2013				Mar. 15, 2016		Nov. 11, 2016	[1]			Dec. 11, 2016	[1]			Oct. 01, 2012	[1]			Feb. 06, 2017	[1]			Jan. 18, 2012				Sep. 04, 2014	[3]			Oct. 05, 2013	[1]			Nov. 11, 2016	[1]			Jan. 18, 2012				Oct. 16, 2014	[4]			Apr. 10, 2011	[3]			Jun. 24, 2012	[8]			Sep. 15, 2011	[8]		Jul. 18, 2013				Jul. 18, 2013				Jun. 09, 2013	[1]			Oct. 18, 2013	[4]				Mar. 01, 2032	[1]				Oct. 16, 2014	[4]			Jul. 01, 2020
Unamortized premium	$ 1,022,000										$ 1,022,000	[9]	$ 1,101,000
Mortgage loans, net of premiums	935,485,000	1,043,188,000									935,485,000	[9]	1,043,188,000	140,186,000	[1],[2]	141,465,000	[1],[2]			80,000,000	[1],[3]	75,325,000	[1]	76,179,000	[1]	65,995,000	[1]	66,437,000	[1]	68,747,000	[10]	66,858,000	[10]	53,443,000	54,157,000	53,967,000	[1]	54,306,000	[1]	53,954,000	[1]	54,296,000	[1]	52,800,000	[1]	52,800,000	[1]	51,832,000	[1]	52,154,000	[1]	44,534,000	[11]	41,430,000	[11]	43,506,000	[11],[3]	40,152,000	[11],[3]	38,921,000	[1]	39,941,000	[1]	39,250,000	[1]	39,496,000	[1]	38,289,000	[11]	35,620,000	[11]	28,944,000	[10],[4]	28,388,000	[10],[4]			19,515,000	[10],[3]	16,576,000	[1],[3]	16,976,000	[1],[3]			16,150,000	15,024,000	[11]	13,978,000	[11]	10,870,000	[11]	10,113,000	[11]	10,000,000	[1]	10,000,000	[1]	9,566,000	[11],[4]	8,900,000	[11],[4]		8,983,000	[1]		9,060,000	[1]	8,805,000	[10],[4]	8,636,000	[10],[4]	4,946,000	5,080,000
Mortgage loans on real estate, number																6
Exchange rate			1.45	1.34	1.45	1.34	1.61	1.56	1.61	1.56
Letter of credit security amount																																																																																																							€ 1,300,000

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

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

[5] If the loan is not repaid by March 1, 2012, the interest rate increases to the greater of 9.62% or the treasury rate then in effect plus 2%. Subject to a prepayment lock-out period through December 2011.

[6] 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.

[7] Two one-year extensions are available, which we may exercise if certain conditions are met.

[8] A one-year extension is available, which we may exercise if certain conditions are met.

[9] 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 June 30, 2011, we had provided limited recourse guarantees with respect to approximately $60.1 million principal amount of the outstanding mortgage indebtedness, and partial letter of credit support with respect to approximately an additional $47.3 million of the outstanding mortgage indebtedness.

[10] Based on exchange rate of $1.61 to £1.00 as of June 30, 2011 and $1.56 to £1.00 as of December 31, 2010.

[11] Based on exchange rate of $1.45 to €1.00 as of June 30, 2011 and $1.34 to €1.00 as of December 31, 2010.