Discontinued operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended				18 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 property		Sep. 30, 2013		Jun. 30, 2014 property	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment	$ 7,648				$ 7,648					$ 7,644
Net assets of discontinued operations
Other assets	20				20					103
Total assets	7,668				7,668					7,747
Total liabilities	(172)				(172)					(266)
Net assets of discontinued operations	7,496				7,496					7,481
Income from discontinued operations, net
Total revenues	0		319		0		4,658
Operating expenses	180		126		489		1,856
Total revenues less operating expenses from discontinued operations	(180)		193		(489)		2,802
Depreciation and Amortization, Discontinued Operations	0		236		0		1,638
(Gain) loss on sale of real estate	0		0		0		121
(Loss) income from discontinued operations	$ (180)	[1]	$ (43)	[1]	$ (489)	[1]	$ 1,043	[1]
Number of operating properties classified as held for sale					4
Number of properties sold									7

[1] includes the results of operations of four properties that were classified as “held for sale” as of September 30, 2014, as well as the results of operations (prior to disposition) and gain on sale of real estate attributable to seven properties sold during the period from January 1, 2013, to September 30, 2014. In October 2014, we completed the sale of one property which was classified as “held for sale” as of September 30, 2014.