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Stock Option and Incentive Plan (Restricted Stock) (Narrative) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) d $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	154,869,198	154,537,378
Stock based compensation expense | $	$ 39,800		$ 33,200
Common Stock, Value, Issued | $	1,548	$ 1,545
Intrinsic Value of stock options | $	$ 16,400
Number Exercisable		540,441	540,441
Exercisable, Weighted Average Exercise Price | $ / shares		$ 96.35	$ 96.35
Non-qualified stock options issued	0	0	0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued	26,503	20,320	37,414
Employee and director payment per share (in dollars per share) | $ / shares	$ 0.01
Common Stock, Value, Issued | $	$ 3,500	$ 2,400	$ 4,900
Common Stock Weighted Average Price (in dollars per share) | $ / shares	$ 131.27	$ 119.27	$ 130.32
LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value Of LTIP Units Issued | $	$ 22,100	$ 22,700	$ 13,600
Weighted Average Per Unit Fair Value (in dollars per share) | $ / shares	$ 121.50	$ 110.29	$ 119.41
Expected life assumed to calculate per unit fair value per LTIP unit (in years)	5 years 8 months 12 days	5 years 8 months 12 days	5 years 8 months 12 days
Risk-free rate	2.68%	2.63%	2.14%
Expected price volatility	27.00%	27.00%	28.00%
LTIP and MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee and director payment per share (in dollars per share) | $ / shares	$ 0.25
Unvested Restricted stock and LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses | $	$ 23,300
Unvested 2017 - 2019 MYLTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expenses | $	$ 12,400
Weighted-average period (years)	2 years 4 months 24 days
Non-Qualified Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance	250,000
Payment Award Discount From Market Price Based on Ten Business Day Average	85.00%
Number Of Days Used In Calculation, Average Closing Prices Of Common Stock | d	10
Number of shares issued	5,862	6,268	6,317
Weighted Average Purchase Price of Shares (in dollars per share) | $ / shares	$ 104.11	$ 107.20	$ 105.97
Boston Properties Limited Partnership | LTIP Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares)	181,919	205,838	113,918
Boston Properties Limited Partnership | MYLTIP 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares)	220,734
Boston Properties Limited Partnership | MYLTIP 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares)		342,659
Boston Properties Limited Partnership | MYLTIP 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
MYLTIP units issued (in shares)			400,000

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