Discontinued Operations - Discontinued operations results of operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Rental revenue	$ 3,440	$ 3,102	$ 9,937	$ 4,609
Revenue reimbursements	200	170	548	469
Total Revenues	5,742	5,035	16,370	10,389
Depreciation, depletion and amortization	1,821	2,804	6,350	3,303
Operating expenses	983	875	2,951	1,312
Property taxes	663	647	1,949	1,384
Management company indirect	550	351	1,366	962
Corporate expenses	522	617	2,910	2,510
Total cost of operations	4,074	5,294	15,061	9,471
Total operating profit (loss)	1,668	(259)	1,309	918
Interest expense	(768)	(783)	(2,418)	(783)
Income (loss) before income taxes	2,538	59,142	727	58,742
Provision for (benefit from) income taxes	508	15,543	269	15,371
Income (loss) from discontinued operations	(78)	1,585	122,109	4,969
Discontinued Operations, Disposed of by Sale [Member]
Rental revenue	190	5,636	9,602	16,634
Revenue reimbursements	29	1,383	2,274	3,713
Total Revenues	219	7,019	11,876	20,347
Depreciation, depletion and amortization	29	1,965	3,131	5,727
Operating expenses	52	1,004	1,694	2,570
Property taxes	19	754	1,266	2,208
Management company indirect	370	209	1,360	542
Corporate expenses	56	0	1,458	0
Total cost of operations	526	3,932	8,909	11,047
Total operating profit (loss)	(307)	3,087	2,967	9,300
Interest expense	0	(468)	(587)	(1,087)
Gain on sale of buildings	200	0	165,007	0
Income (loss) before income taxes	(107)	2,619	167,387	8,213
Provision for (benefit from) income taxes	(29)	1,034	45,278	3,244
Income (loss) from discontinued operations	$ (78)	$ 1,585	$ 122,109	$ 4,969