Discontinued operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				15 Months Ended
	Mar. 31, 2014 property		Mar. 31, 2013		Mar. 31, 2014 property	Dec. 31, 2013
Net assets of discontinued operations
Properties "held for sale, "net	$ 7,653				$ 7,653	$ 7,644
Other assets	157				157	103
Total assets	7,810				7,810	7,747
Total liabilities	(132)				(132)	(266)
Net assets of discontinued operations	7,678				7,678	7,481
Income from discontinued operations, net
Total revenues	0		3,792
Operating expenses	(162)		(1,449)
Total revenues less operating expenses from discontinued operations	(162)		2,343
Depreciation expense	0		(1,166)
Loss on sale of real estate	0		(340)
(Loss) income from discontinued operations	$ (162)	[1]	$ 837	[1]
Number of operating properties classified as held for sale	4
Number of properties sold					7

[1] (Loss) income from discontinued operations includes the results of operations of four properties that were classified as “held for sale” as of March 31, 2014, as well as the results of operations (prior to disposition) and loss on sale of real estate attributable to seven properties sold during the period from January 1, 2013, to March 31, 2014.