Overview (Details)	Mar. 31, 2013 Number_of_Parcels_of_Land Number_of_Properties
Overview [Line Items]
Number of office properties owned	58
Number of multifamily properties owned	9
Number of land parcels	2
Wholly Owned Consolidated Office Properties [Member]
Overview [Line Items]
Number of office properties owned	50
Partially Owned Unconsolidated Office Properties [Member]
Overview [Line Items]
Number of office properties owned	8

Number of parcels of land subject to ground rent, in which we own fee interests as of the balance sheet date.

No definition available.

Name:	dei_NumberOfLandParcels
Namespace Prefix:	dei_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	instant