Real Estate (Narrative) (Details) $ / shares in Units, $ in Thousands					1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 25, 2021 USD ($) ft² $ / shares	Jun. 07, 2021 USD ($) a ft² Buildings	Jun. 02, 2021 USD ($) ft² Buildings	Apr. 19, 2021 USD ($) a ft²	Jun. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 29, 2021 USD ($) ft²	Apr. 16, 2021 ft²	Feb. 25, 2021 ft²	Feb. 01, 2021 ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Real Estate Properties [Line Items]
Total revenue						$ 713,807	$ 654,773	$ 1,427,502	$ 1,407,329
Cash and Cash Equivalents, at Carrying Value					$ 557,307	557,307	1,691,047	557,307	1,691,047					$ 1,668,742	$ 644,950
Cash held in escrows					79,973	79,973	300,608	79,973	300,608					50,587	46,936
11251 Roger Bacon Drive
Real Estate Properties [Line Items]
Leased percentage				100.00%
Net Rentable Area (in sf) | ft²				65,000
Area of Land | a				2.6
11251 Roger Bacon Drive | Scenario, Plan
Real Estate Properties [Line Items]
Payments to Acquire Real Estate				$ 5,600
153 & 211 Second Avenue [Member]
Real Estate Properties [Line Items]
Payments to Acquire Real Estate			$ 100,200
Number of real estate properties | Buildings			2
Leased percentage			100.00%
Net Rentable Area (in sf) | ft²			137,000
Total revenue					800
Operating Income (Loss)					(300)
One Five Nine East 53rd Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²													220,000
Noncontrolling Interest, Ownership Percentage by Parent													55.00%
Shady Grove Bio+Tech Campus
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²		435,000
Area of Land | a		31
Cash and Cash Equivalents, at Carrying Value		$ 10,000
Number of buildings | Buildings		7
Shady Grove Bio+Tech Campus | Scenario, Plan
Real Estate Properties [Line Items]
Payments to Acquire Real Estate		$ 116,500
360 Park South Avenue
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²	450,000
Cash held in escrows	$ 30,000
360 Park South Avenue | Scenario, Plan
Real Estate Properties [Line Items]
Noncash or Part Noncash Acquisition, Value of Assets Acquired	300,000
Noncash or Part Noncash Acquisition, Debt Assumed	202,000
Other Significant Noncash Transaction, Value of Consideration Given	$ 98,000
360 Park South Avenue | Minimum [Member] | Scenario, Plan
Real Estate Properties [Line Items]
Closing price of common stock (in dollars per share) | $ / shares	$ 111.00
Safeco Plaza
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²										800,000
Cash and Cash Equivalents, at Carrying Value										$ 46,500
3625 - 3635 Peterson Way
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²											218,000
6595 Springfield Center Drive
Real Estate Properties [Line Items]
Gains (Losses) on Sales of Investment Real Estate						7,800
Construction in Progress | 180 CityPoint
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²												329,000
Construction in Progress | 880 Winter Street [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²												224,000
Construction in Progress | The Prudential Center Observatory
Real Estate Properties [Line Items]
Net Rentable Area (in sf) | ft²												59,000
Boston Properties Limited Partnership
Real Estate Properties [Line Items]
Total revenue						713,807	654,773	1,427,502	1,407,329
Cash and Cash Equivalents, at Carrying Value					557,307	557,307	1,691,047	557,307	1,691,047					1,668,742	644,950
Cash held in escrows					$ 79,973	$ 79,973	$ 300,608	$ 79,973	$ 300,608					$ 50,587	$ 46,936