Noncontrolling Interest - Common Shares and Units Activity (Details)	12 Months Ended
Dec. 31, 2020 shares
Equity Commonwealth
Increase (Decrease) in Stockholders' Equity
Noncontrolling ownership interest in the Operating Trust	0.20%
Common Shares, OP Units and LTIP Units
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)	121,972,859
Redemption of shares (in shares)	(895,068)
OP Unit Redemption (in shares)	(1,000)
Restricted share grants, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares)	689,280
Ending balance (in shares)	121,766,071
Common Shares
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)	121,924,199
Redemption of shares (in shares)	(895,068)
OP Unit Redemption (in shares)	0
Restricted share grants, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares)	493,424
Ending balance (in shares)	121,522,555
OP Units and LTIP Units \| Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)	48,660
Redemption of shares (in shares)	0
OP Unit Redemption (in shares)	(1,000)
Restricted share grants, time-based LTIP Unit grants and vested restricted stock units, net of forfeitures (in shares)	195,856
Ending balance (in shares)	243,516

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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Number of shares issued which are neither cancelled nor held in the treasury.

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Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).

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Number of stock bought back by the entity at the exercise price or redemption price.

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Number of shares that have been repurchased and retired during the period.

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