This element represents the amount of gain (loss) on sale of properties during the reporting period net of the applicable income taxes realized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 974

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-15.(a)(1)(ii))

-URI http://asc.fasb.org/extlink&oid=6875705&loc=d3e641549-123027

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 15

-Paragraph a

-Subparagraph 1(ii)

-Article 3

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

Dispositions of properties (Details) - USD ($) $ in Thousands				3 Months Ended	6 Months Ended
	May. 13, 2015	Mar. 31, 2015	Feb. 23, 2015	Jun. 30, 2015	Jun. 30, 2015
Gain (loss) on sale of property
Gain (loss) on sale of property				$ 948	$ 11,410
Office Property in Plano, Texas
Gain (loss) on sale of property
Gain (loss) on sale of property			$ 1,500
Office Property in Eden Prairie, Minnesota
Gain (loss) on sale of property
Gain (loss) on sale of property		$ 9,000
Office Property in Charlotte, North Carolina
Gain (loss) on sale of property
Gain (loss) on sale of property	$ 900