CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 272,908	$ 29,666	$ 232,894
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivative instruments and other assets	456	(248)	3,479
Unrealized gain, net on marketable securities	1,199	361	0
Total comprehensive income	274,563	29,779	236,373
Comprehensive income attributable to the noncontrolling interest	(95)	(10)	0
Total comprehensive income attributable to Equity Commonwealth	$ 274,468	$ 29,769	$ 236,373