CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 242,377	$ 37,047	$ 452,974	$ 224,709
Other comprehensive income, net of tax:
Unrealized gain on derivative instruments	0	339	0	456
Unrealized gain on marketable securities	0	298	342	72
Total comprehensive income	242,377	37,684	453,316	225,237
Comprehensive income attributable to the noncontrolling interest	(91)	(14)	(170)	(77)
Total comprehensive income attributable to Equity Commonwealth	$ 242,286	$ 37,670	$ 453,146	$ 225,160