Noncontrolling Interest - Common Shares and Units Activity (Details)	3 Months Ended
	Mar. 31, 2021 shares
Equity Commonwealth
Increase (Decrease) in Stockholders' Equity
Ownership percentage by noncontrolling owners	0.20%
Common Shares
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period (in shares)	121,522,555
Repurchase of shares (in shares)	(210,334)
Share-based compensation grants and vesting, net of forfeitures (in shares)	604,654
Balance as of end of period (in shares)	121,916,875
OP Units and LTIP Units | Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period (in shares)	243,516
Repurchase of shares (in shares)	0
Share-based compensation grants and vesting, net of forfeitures (in shares)	0
Balance as of end of period (in shares)	243,516
Common Stock, OP Units, and LTIP Units
Increase (Decrease) in Stockholders' Equity
Balance as of beginning of period (in shares)	121,766,071
Repurchase of shares (in shares)	(210,334)
Share-based compensation grants and vesting, net of forfeitures (in shares)	604,654
Balance as of end of period (in shares)	122,160,391