Rental Income - Narrative (Details)	3 Months Ended
Mar. 31, 2018
Minimum
Operating Leases [Line Items]
Term of lease	1 year
Maximum
Operating Leases [Line Items]
Term of lease	21 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