9. Debt (Details)	12 Months Ended
Dec. 31, 2015 USD ($)
6.5% Notes Due September 2017
Common Stock Sold in Private Placement, Value	$ 3,200,000

Monetary value of the issuance of new units of limited partnership interest in a private placement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

Name:	us-gaap_PartnersCapitalAccountPrivatePlacementOfUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration