CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 210,597	$ 187,662
Other comprehensive income (loss), net of tax:
Unrealized gain on derivative instruments	0	117
Unrealized gain (loss) on marketable securities	342	(226)
Total comprehensive income	210,939	187,553
Comprehensive income attributable to the noncontrolling interest	(79)	(63)
Total comprehensive income attributable to Equity Commonwealth	$ 210,860	$ 187,490