Secured and unsecured senior debt Outstanding consolidated indebtedness (Details) (USD $)											12 Months Ended																												0 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended			1 Months Ended		7 Months Ended	12 Months Ended								12 Months Ended
	Dec. 31, 2013		Dec. 31, 2013 2014	Dec. 31, 2013 2015	Dec. 31, 2013 2016	Dec. 31, 2013 2017	Dec. 31, 2013 2018	Dec. 31, 2013 Thereafter	Dec. 31, 2013 Secured notes payable		Dec. 31, 2013 Secured notes payable from insurance co. maturing on 4/1/14		Dec. 31, 2013 Secured notes payable from bank maturing on 7/1/14		Dec. 31, 2013 Secured notes payable from bank maturing on 11/1/14		Dec. 31, 2013 Other secured notes payable maturing on 11/18/14		Dec. 31, 2013 Secured notes payable from bank maturing on 6/1/15		Dec. 31, 2013 Secured notes payable maturing on 7/1/15 Extension_Option		Dec. 31, 2013 CMBS maturing on 1/1/16		Dec. 31, 2013 CMBS maturing on 4/1/16		Dec. 31, 2013 Secured notes payable maturing on 06/1/16 Extension_Option		Dec. 31, 2013 CMBS maturing on 8/1/16		Dec. 31, 2013 Secured Debt from Bank Maturing on 20 January 2017		Dec. 31, 2013 Secured notes payable maturing on 8/23/17		Dec. 31, 2013 Secured Debt Other Maturing 1 April 2020		Dec. 31, 2013 Secured notes payable from bank maturing on 6/1/37		Jul. 26, 2013 2016 Unsecured Senior Bank Term Loan	Aug. 30, 2013 2016 Unsecured Senior Bank Term Loan	Dec. 31, 2013 2016 Unsecured Senior Bank Term Loan		Aug. 30, 2013 2019 Unsecured Senior Bank Term Loan	Dec. 31, 2013 2019 Unsecured Senior Bank Term Loan		Jul. 31, 2013 2019 Unsecured Senior Bank Term Loan	Aug. 30, 2013 $1.5 billion unsecured senior line of credit	Apr. 30, 2012 $1.5 billion unsecured senior line of credit	Jul. 31, 2013 $1.5 billion unsecured senior line of credit	Dec. 31, 2013 $1.5 billion unsecured senior line of credit		Dec. 31, 2013 4.60% unsecured senior notes payable		Dec. 31, 2013 3.90% unsecured senior notes payable		Jun. 30, 2012 Secured notes payable maturing on 7/1/15 Construction Loans	Dec. 31, 2013 Alexandria Technology Square®	Dec. 31, 2013 Other Ownership Interest Alexandria Technology Square®	Dec. 31, 2013 Federal Funds Rate $1.5 billion unsecured senior line of credit	Feb. 28, 2014 Subsequent Event Secured notes payable maturing on 06/1/16
Summary of fixed rate/hedged and floating rate debt
Fixed Rate/Hedged Variable Rate	$ 2,584,808,000		$ 229,138,000	$ 12,693,000	$ 583,143,000	$ 1,668,000	$ 1,809,000	$ 1,756,357,000	$ 586,578,000																																$ 350,000,000			$ 600,000,000						$ 0		$ 549,603,000		$ 498,627,000
Unhedged Variable rate	476,253,000		240,000	46,013,000	150,000,000	76,000,000	0	204,000,000	122,253,000																																150,000,000			0						204,000,000		0		0
Principal amount	3,061,061,000		229,378,000	58,706,000	733,143,000	77,668,000	1,809,000	1,960,357,000	708,831,000																																500,000,000			600,000,000						204,000,000		549,603,000		498,627,000						2,200,000
Stated interest rate (as a percent)									5.39%		5.26%		6.05%		5.39%		6.00%		5.64%				5.73%		5.82%				6.35%		2.16%				7.75%		6.50%															4.60%		3.90%
Base rate																					LIBOR						LIBOR						LIBOR						LIBOR	LIBOR	LIBOR		LIBOR	LIBOR			LIBOR		LIBOR	LIBOR	[1]								federal funds rate
Basis spread on LIBOR (as a percent)																					1.50%						1.40%						1.35%						1.75%		1.20%			1.20%		1.50%			1.20%	1.10%	[1]								0.50%
Effective rate (as a percent)	3.76%	[2]							5.45%	[2]	5.59%	[2]	4.88%	[2]	4.00%	[2]	6.00%	[2]	4.50%	[2]	1.67%	[2]	5.73%	[2]	5.82%	[2]	1.57%	[2]	6.35%	[2]	2.16%	[2]	1.52%	[2]	7.75%	[2]	6.50%	[2]			2.37%	[2]		2.85%	[2]					1.27%	[2]	4.61%	[2]	3.94%	[2]
Maturity date											Apr. 01, 2014	[3]	Jul. 01, 2014	[3]	Nov. 01, 2014	[3]	Nov. 18, 2014	[3]	Jun. 01, 2015	[3]	Jul. 01, 2015	[3],[4]	Jan. 01, 2016	[3]	Apr. 01, 2016	[3]	Jun. 01, 2016	[3],[5]	Aug. 01, 2016	[3]	Jan. 20, 2017	[3]	Aug. 23, 2017	[3],[6]	Apr. 01, 2020	[3]	Jun. 01, 2037	[3]			Jul. 31, 2016	[3]		Jan. 03, 2019	[3]					Jan. 03, 2019	[3]	Apr. 01, 2022	[3]	Jun. 15, 2023	[3]
Partner interest in project (in percent)																																																										10.00%
Partner contribution to the repayment of debt																																																										20,900,000
Aggregate commitments of construction loan																					55,000,000						36,000,000						250,400,000																							55,000,000
Number of extensions available under line of credit																					2						2
Number of one-year extension options																					2						2
Annual facility fee (as a percent)																																															0.20%	0.20%	0.25%	0.20%
Future principal payments due on secured and unsecured debt
2014									229,577,000		208,683,000	[7]	6,446,000		7,480,000		240,000		127,000		0		1,713,000		931,000		0		2,487,000		0		0		1,453,000		17,000				0			0						0		0		0
2015									58,845,000		0		0		0		0		5,788,000		46,013,000		1,816,000		988,000		0		2,652,000		0		0		1,570,000		18,000				0			0						0		0		0
2016									233,320,000		0		0		0		0		0		0		75,501,000		29,389,000		0		126,715,000		0		0		1,696,000		19,000				500,000,000			0						0		0		0
2017									77,852,000		0		0		0		0		0		0		0		0		0		0		76,000,000		0		1,832,000		20,000				0			0						0		0		0
2018									2,001,000		0		0		0		0		0		0		0		0		0		0		0		0		1,979,000		22,000				0			0						0		0		0
Thereafter									107,242,000		0		0		0		0		0		0		0		0		0		0		0		0		106,491,000		751,000				0			600,000,000						204,000,000		550,000,000		500,000,000
Unamortized discount	(1,776,000)		(199,000)	(139,000)	(177,000)	(184,000)	(192,000)	(885,000)																																																	(226,000)
Principal amount	3,062,837,000		229,577,000	58,845,000	733,320,000	77,852,000	2,001,000	1,961,242,000	708,837,000		208,683,000		6,446,000		7,480,000		240,000		5,915,000		46,013,000		79,030,000		31,308,000		0		131,854,000		76,000,000		0		115,021,000		847,000				500,000,000			600,000,000						204,000,000		550,000,000		500,000,000
Total consolidated debt, Effective Interest	3.76%
Balloon payments	3,037,202,000		221,080,000	51,741,000	730,029,000	76,000,000	0	1,958,352,000
Principal amortization	$ 23,859,000		$ 8,298,000	$ 6,965,000	$ 3,114,000	$ 1,668,000	$ 1,809,000	$ 2,005,000

[1] In addition to the stated rate, the line of credit is subject to an annual facility fee of 0.20%.

[2] Represents the weighted average contractual interest rate as of the end of the period plus the impact of debt premiums/discounts and interest rate swap agreements. The weighted average interest rate excludes bank fees and amortization of loan fees.

[3] Includes any extension options that we control.

[4] Secured construction loan with aggregate commitments of $55.0 million. We have two, one-year options to extend the stated maturity date to July 1, 2017, subject to certain conditions.

[5] Secured construction loan with aggregate commitments of $36.0 million. We have two, one-year options to extend the stated maturity date to June 1, 2018, subject to certain conditions.

[6] Secured construction loan with aggregate commitments of $250.4 million. We have a one-year option to extend the stated maturity date to August 23, 2018, subject to certain conditions. We expect to begin drawing on this loan in the first quarter of 2014.

[7] Secured note payable related to Alexandria Technology Square® was repaid on January 31, 2014. Our partner has a 10% interest in this project and provided $20.9 million for the repayment.