Segments - Reconciliation of Net Operating Income to Net Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net operating income	$ 7,980	$ 6,858	$ 24,713	$ 19,567
Depreciation and amortization	(9,239)	(8,885)	(28,018)	(25,636)
General and administrative expenses	(2,098)	(2,156)	(7,762)	(6,864)
Acquisition, development and other pursuit costs	(61)	(345)	(477)	(1,486)
Impairment charges	(19)	(149)	(50)	(184)
Interest income	1,910	1,024	4,966	1,928
Interest expense	(4,253)	(4,124)	(13,282)	(11,893)
Loss on extinguishment of debt	0	(82)	0	(82)
Gain on real estate dispositions	4,692	3,753	8,087	30,440
Change in fair value of interest rate derivatives	87	498	300	(2,264)
Other income	74	35	154	154
Income tax provision	(29)	(16)	(781)	(240)
Net income	10,461	7,946	24,157	37,610
Operating Segments
Net operating income	19,397	18,393	61,020	53,737
Segment Reconciling Items
Depreciation and amortization	(9,239)	(8,885)	(28,018)	(25,636)
General and administrative expenses	(2,098)	(2,156)	(7,762)	(6,864)
Acquisition, development and other pursuit costs	(61)	(345)	(477)	(1,486)
Impairment charges	(19)	(149)	(50)	(184)
Interest income	1,910	1,024	4,966	1,928
Interest expense	(4,253)	(4,124)	(13,282)	(11,893)
Loss on extinguishment of debt	0	(82)	0	(82)
Gain on real estate dispositions	4,692	3,753	8,087	30,440
Change in fair value of interest rate derivatives	87	498	300	(2,264)
Other income	74	35	154	154
Income tax provision	$ (29)	$ (16)	$ (781)	$ (240)