CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 187,662	$ 23,822
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivative instruments	117	(153)
Unrealized loss on marketable securities	(226)	(641)
Total comprehensive income	187,553	23,028
Comprehensive income attributable to the noncontrolling interest	(63)	(8)
Total comprehensive income attributable to Equity Commonwealth	$ 187,490	$ 23,020