Discontinued Operations - Discontinued operations results of operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Lease revenue	$ 3,581	$ 3,617	$ 10,796	$ 10,418
Depreciation, depletion and amortization	1,431	1,821	4,390	6,350
Operating expenses	952	983	2,744	2,951
Property taxes	740	663	2,206	1,949
Management company indirect	670	550	1,872	1,366
Corporate expenses	732	522	1,928	2,910
Total cost of operations	4,525	4,074	13,140	15,061
Total operating profit (loss)	1,358	1,668	4,820	1,309
Interest expense	(129)	(768)	(989)	(2,418)
Income (loss) before income taxes	2,628	2,538	9,024	727
Provision for (benefit from) income taxes	726	508	2,529	269
Income (loss) from discontinued operations	$ (13)	$ (78)	$ 6,849	$ 122,109
Earnings per common share:
Basic earnings per common share Discontinued operations	$ 0.00	$ (0.01)	$ 0.69	$ 12.17
Diluted earnings per common share discontinued operations	$ 0.00	$ (0.01)	$ 0.69	$ 12.08
Discontinued Operations, Disposed of by Sale [Member]
Lease revenue	$ 0	$ 219	$ 460	$ 11,876
Depreciation, depletion and amortization	(24)	29	17	3,131
Operating expenses	12	52	246	1,694
Property taxes	0	19	46	1,266
Management company indirect	0	370	0	1,360
Corporate expenses	0	56	0	1,458
Total cost of operations	(12)	526	309	8,909
Total operating profit (loss)	12	(307)	151	2,967
Interest expense	0	0	0	(587)
Gain (loss) on sale of buildings	(30)	200	9,238	165,007
Income (loss) before income taxes	(18)	(107)	9,389	167,387
Provision for (benefit from) income taxes	(5)	(29)	2,540	45,278
Income (loss) from discontinued operations	$ (13)	$ (78)	$ 6,849	$ 122,109
Earnings per common share:
Basic earnings per common share Discontinued operations	$ 0.00	$ (0.01)	$ 0.69	$ 12.17
Diluted earnings per common share discontinued operations	$ 0.00	$ (0.01)	$ 0.69	$ 12.08