Earnings Per Common Share (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) $ / shares shares
Numerator for earnings per common share - basic:
Net income	$ 25,458
Net income attributable to noncontrolling interest	(53)
Preferred distributions	(1,997)
Net income attributable to Equity Commonwealth common shareholders	23,408
Numerator for earnings per common share - diluted:
Net income	25,458
Net income attributable to noncontrolling interest	(53)
Preferred distributions	(1,997)
Numerator for net income per share - diluted	$ 23,408
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding — basic (in shares) | shares	107,216
Weighted average number of common shares outstanding — diluted (in shares) | shares	108,224
Net income per common share attributable to Equity Commonwealth common shareholders:
Basic (in dollars per share) | $ / shares	$ 0.22
Diluted (in dollars per share) | $ / shares	$ 0.22
Anti-dilutive securities:
Preferred shares, dividend percentage	6.50%
Weighted average number of shares, restricted stock units, unvested (in shares) | shares	129
Series D Preferred Stock
Anti-dilutive securities:
Effect of anti-dilutive securities (in shares) | shares	4,032
LTIP and OP units
Anti-dilutive securities:
Effect of anti-dilutive securities (in shares) | shares	223
RSUs
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding, dilutive adjustment (in shares) | shares	898
LTIP Units
Denominator for earnings per common share - basic and diluted:
Weighted average number of common shares outstanding, dilutive adjustment (in shares) | shares	110