Segment Information - Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue
Rental revenue	$ 14,393	$ 15,695
Expenses
Property operating	665	286
General and administrative	1,478	1,699
Acquisition-related	127	185
Amortization	3,517	4,022
Impairments	204
Total expenses	5,991	6,192
Total other income and expenses	(1,070)	(2,686)
Income before income tax expense	7,332	6,817
Income tax expense (benefit)	122	76
Net income	7,210	6,741
Operating Segments | Wireless Communication
Revenue
Rental revenue	7,236	9,645
Expenses
Property operating	51	34
Amortization	2,361	3,072
Total expenses	2,412	3,106
Total other income and expenses	5,820	171
Income before income tax expense	10,644	6,710
Net income	10,644	6,710
Operating Segments | Outdoor Advertising
Revenue
Rental revenue	5,081	4,210
Expenses
Property operating	260	171
Amortization	987	793
Impairments	204
Total expenses	1,451	964
Total other income and expenses	61	64
Income before income tax expense	3,691	3,310
Net income	3,691	3,310
Operating Segments | Renewable Power Generation
Revenue
Rental revenue	2,076	1,840
Expenses
Property operating	354	81
Amortization	169	157
Total expenses	523	238
Total other income and expenses	203	203
Income before income tax expense	1,756	1,805
Net income	1,756	1,805
Corporate
Expenses
General and administrative	1,478	1,699
Acquisition-related	127	185
Total expenses	1,605	1,884
Total other income and expenses	(7,154)	(3,124)
Income before income tax expense	(8,759)	(5,008)
Income tax expense (benefit)	122	76
Net income	$ (8,881)	$ (5,084)