CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 452,093	$ 492,866	$ 272,908
Other comprehensive income, net of tax:
Unrealized gain on derivative instruments	0	0
Unrealized gain on derivative instruments			456
Unrealized gain, net on marketable securities	0	342	1,199
Total comprehensive income	452,093	493,208	274,563
Comprehensive income attributable to noncontrolling interest	(799)	(186)	(95)
Total comprehensive income attributable to Equity Commonwealth	$ 451,294	$ 493,022	$ 274,468