Leasing Operations (Narrative) (Details)	12 Months Ended
Dec. 31, 2017
Small Tenant [Member]
Operating Leased Assets [Line Items]
Lease Term	1 year
Large Tenant [Member]
Operating Leased Assets [Line Items]
Lease Term	25 years

Term of the lessor's leasing arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_LessorLeasingArrangementsOperatingLeasesTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration