Lease Intangibles - Schedule of Amortization of Lease Intangibles (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases [Abstract]
Amortization of acquired in-place leases, Depreciation and amortization	$ 7,220	$ 14,598	$ 26,787
Amortization of above and below market leases, Increase (decrease) to rental income	$ (1,774)	$ (6,531)	$ (7,515)

Aggregate amount of intangible asset amortization recognized as expense during the period included under depreciation and amortization.

No definition available.

Name:	eqc_FiniteLivedIntangibleAssetsAmortizationExpenseIncludedInDepreciationAndAmortization
Namespace Prefix:	eqc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration