Discontinued Operations - Discontinued operations results of operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Lease revenue	$ 3,730	$ 3,498	$ 7,215	$ 6,801
Depreciation, depletion and amortization	1,472	2,131	2,959	4,529
Operating expenses	910	1,103	1,792	1,968
Property taxes	713	611	1,466	1,286
Management company indirect	610	455	1,202	816
Corporate expenses	551	1,709	1,196	2,388
Total cost of operations	4,256	6,009	8,615	10,987
Total operating profit	2,107	(456)	3,462	(359)
Interest expense	(272)	(807)	(860)	(1,650)
Income before income taxes	4,083	(1,058)	6,396	(1,811)
Provision for income taxes	1,131	(179)	1,803	(239)
Income from discontinued operations	$ 6,776	$ 120,465	$ 6,862	$ 122,187
Earnings per common share:
Basic earnings per common share Discontinued operations	$ 0.68	$ 12.01	$ 0.69	$ 12.19
Diluted earnings per common share discontinued operations	$ 0.68	$ 11.92	$ 0.69	$ 12.10
Discontinued Operations, Disposed of by Sale [Member]
Lease revenue	$ 222	$ 4,110	$ 460	$ 11,657
Depreciation, depletion and amortization	12	1,217	41	3,102
Operating expenses	139	464	234	1,642
Property taxes	26	449	46	1,247
Management company indirect	0	812	0	990
Corporate expenses	0	655	0	1,402
Total cost of operations	177	3,597	321	8,383
Total operating profit	45	513	139	3,274
Interest expense	0	(187)	0	(587)
Gain on sale of buildings	9,245	164,807	9,268	164,807
Income before income taxes	9,290	165,133	9,407	167,494
Provision for income taxes	2,514	44,668	2,545	45,307
Income from discontinued operations	$ 6,776	$ 120,465	$ 6,862	$ 122,187
Earnings per common share:
Basic earnings per common share Discontinued operations	$ 0.68	$ 12.01	$ 0.69	$ 12.19
Diluted earnings per common share discontinued operations	$ 0.68	$ 11.92	$ 0.69	$ 12.10