Discontinued Operations - Discontinued operations results of operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lease revenue	$ 3,447	$ 3,730	$ 7,045	$ 7,215
Depreciation, depletion and amortization	1,500	1,472	2,968	2,959
Operating expenses	781	910	1,706	1,792
Property taxes	646	713	1,383	1,466
Total operating profit	1,204	2,107	1,998	3,462
Interest expense	(45)	(272)	(96)	(860)
Income before income taxes	5,515	4,083	7,615	6,396
Provision for income taxes	1,538	1,131	2,139	1,803
Income from discontinued operations	$ 0	$ 6,776	$ 0	$ 6,862
Earnings per common share:
Basic earnings per common share Discontinued operations	$ 0.00	$ 0.68	$ 0.00	$ 0.69
Diluted earnings per common share discontinued operations	$ 0.00	$ 0.68	$ 0.00	$ 0.69
Discontinued Operations, Disposed of by Sale [Member]
Lease revenue		$ 222		$ 460
Depreciation, depletion and amortization		12		41
Operating expenses		139		234
Property taxes		26		46
Management company indirect		0		0
Corporate expenses		0		0
Total cost of operations		177		321
Total operating profit		45		139
Interest expense		0		0
Gain on sale of buildings		9,245		9,268
Income before income taxes		9,290		9,407
Provision for income taxes		2,514		2,545
Income from discontinued operations		$ 6,776		$ 6,862
Earnings per common share:
Basic earnings per common share Discontinued operations		$ 0.68		$ 0.69
Diluted earnings per common share discontinued operations		$ 0.68		$ 0.69