Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) (USD $) In Thousands, unless otherwise specified			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Square 407 Limited Partnership [Member]	Mar. 31, 2014 The Metropolitan Square Associates LLC [Member]	Mar. 31, 2014 BP/CRF 901 New York Avenue LLC [Member]		Mar. 31, 2014 WP Project Developer LLC [Member]		Mar. 31, 2014 Boston Properties Office Value-Added Fund, L.P. [Member]		Mar. 31, 2014 Annapolis Junction NFM, LLC [Member] Buildings Land_Parcels		Mar. 31, 2014 2 GCT Venture LLC [Member]		Mar. 31, 2014 540 Madison Venture LLC [Member]	Mar. 31, 2014 125 West 55th Street Venture LLC [Member]		Mar. 31, 2014 500 North Capitol LLC [Member]	Mar. 31, 2014 Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Properties			Market Square North	Metropolitan Square	901 New York Avenue	[1]	Wisconsin Place Land and Infrastructure	[2]	N/A	[3]	Annapolis Junction	[4]	N/A		540 Madison Avenue	N/A	[5]	500 North Capitol Street, NW
Equity Method Investment, Ownership Percentage			50.00%	51.00%	25.00%	[1]	33.30%	[2]	39.50%	[6]	50.00%	[3]	60.00%	[4]	60.00%	60.00%	[5]	30.00%	33.30%
Carrying value of the Company's investments in unconsolidated joint ventures	$ 127,356	$ 126,084	$ (9,758)	$ 6,236	$ (2,509)		$ 46,944		$ (30)		$ 17,528		$ (91)		$ 69,002	$ 944		$ (910)
Number of real estate properties											2
Number of buildings under construction											1
Parcels of undeveloped land											2

[1] The Company’s economic ownership can increase based on the achievement of certain return thresholds.

[2] The Company’s wholly-owned entity that owns the office component of the project also owns a 33.3% interest in the entity owning the land, parking garage and infrastructure of the project.

[3] Comprised of two buildings, one building under construction and two undeveloped land parcels (See also Note 12).

[4] Two Grand Central Tower was sold on October 25, 2011.

[5] 125 West 55th Street was sold on May 30, 2013.

[6] The Company acquired Mountain View Research Park and Mountain View Technology Park from the Value-Added Fund on April 10, 2013.