Segments - Reconciliation of Net Operating Income to Net Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information
Net operating income	$ 28,869	$ 29,359	$ 26,333	$ 21,806	$ 21,114	$ 19,964	$ 19,908	$ 20,098
Depreciation and amortization									$ (54,564)	$ (39,913)	$ (37,321)
Amortization of right-of-use assets - finance leases									(377)
General and administrative expenses									(12,392)	(11,431)	(10,435)
Acquisition, development and other pursuit costs									(844)	(352)	(648)
Impairment charges									(252)	(1,619)	(110)
Gain on real estate dispositions									4,699	4,254	8,087
Interest income									23,215	10,729	7,077
Interest expense on indebtedness									(30,776)	(19,087)	(17,439)
Interest expense on finance leases									(568)	0	0
Equity in income of unconsolidated real estate entities									273	372	0
Change in fair value of interest rate derivatives									(3,599)	(951)	1,127
Other income (expense), net									585	377	81
Income tax benefit (provision)									491	29	(725)
Net income	$ 7,855	$ 12,063	$ 5,826	$ 6,514	$ 4,895	$ 5,669	$ 5,945	$ 6,983	32,258	23,492	29,925
Operating Segments
Segment Reporting Information
Net operating income									106,367	81,084	80,231
Segment Reconciling Items
Segment Reporting Information
Depreciation and amortization									(54,564)	(39,913)	(37,321)
Amortization of right-of-use assets - finance leases									(377)	0	0
General and administrative expenses									(12,392)	(11,431)	(10,435)
Acquisition, development and other pursuit costs									(844)	(352)	(648)
Impairment charges									(252)	(1,619)	(110)
Gain on real estate dispositions									4,699	4,254	8,087
Interest income									23,215	10,729	7,077
Interest expense on indebtedness									(30,776)	(19,087)	(17,439)
Interest expense on finance leases									(568)	0	0
Equity in income of unconsolidated real estate entities									273	372	0
Loss on extinguishment of debt									0	(11)	(50)
Change in fair value of interest rate derivatives									(3,599)	(951)	1,127
Other income (expense), net									585	388	131
Income tax benefit (provision)									$ 491	$ 29	$ (725)