CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 37,047	$ (5,811)	$ 224,709	$ 18,011
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivative instruments	339	(108)	456	(261)
Unrealized gain on marketable securities	298	2,345	72	1,704
Total comprehensive income (loss)	37,684	(3,574)	225,237	19,454
Comprehensive (income) loss attributable to the noncontrolling interest	(14)	2	(77)	(6)
Total comprehensive income (loss) attributable to Equity Commonwealth	$ 37,670	$ (3,572)	$ 225,160	$ 19,448