Business Segments - Business segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 9,322	$ 9,615
Operating profit	3,404	3,509
Interest expense	248	415
Depreciation, depletion and amortization	2,059	1,929
Cash items	106	0	$ 0	$ 0
Total identifiable net assets	269,517		266,560
Asset Management
Segment Reporting Information [Line Items]
Revenues	7,285	7,574
Operating profit before corporate expenses	3,501	3,423
Corporate expenses	(753)	(520)
Interest expense	248	415
Capital expenditures	2,259	473
Depreciation, depletion and amortization	1,965	1,835
Total identifiable net assets	168,339		169,736
Mining royalty lands
Segment Reporting Information [Line Items]
Revenues	1,762	1,778
Operating profit before corporate expenses	1,625	1,649
Corporate expenses	(66)	(75)
Capital expenditures	0	4
Depreciation, depletion and amortization	39	31
Total identifiable net assets	39,087		39,259
Land Development and Construction
Segment Reporting Information [Line Items]
Revenues	275	263
Operating profit before corporate expenses	(395)	(555)
Corporate expenses	(508)	(413)
Capital expenditures	1,470	479
Depreciation, depletion and amortization	55	63
Total identifiable net assets	58,901		57,126
Corporate
Segment Reporting Information [Line Items]
Total identifiable net assets	3,084		$ 439
Total Segments
Segment Reporting Information [Line Items]
Revenues	9,322	9,615
Operating profit	3,404	3,509
Corporate expenses	(1,327)	(1,008)
Capital expenditures	3,729	956
Depreciation, depletion and amortization	$ 2,059	$ 1,929