Segment Information - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 80,826	$ 107,611
Gain on asset sales	21,925	2,066
Operating and maintenance expenses (including affiliates)	34,650	40,497
Depreciation, depletion and amortization	14,743	25,392
Asset impairment	2,030	0
Interest expense, net	(23,729)	(22,928)
Net income (loss)	23,427	17,489
Total assets	1,624,893		$ 1,670,035
Corporate and Financing
Segment Reporting Information [Line Items]
Revenues	0	0
Gain on asset sales	0	0
Operating and maintenance expenses (including affiliates)	0	0
Depreciation, depletion and amortization	0	0
Asset impairment	0
Interest expense, net	(23,729)	(22,928)
Net income (loss)	(27,901)	(26,299)
Total assets	20,083		961
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	0
Coal, Hard Mineral Royalty and Other
Segment Reporting Information [Line Items]
Revenues	28,476	34,449
Coal, Hard Mineral Royalty and Other | Operating Segments
Segment Reporting Information [Line Items]
Revenues	39,045	53,510
Gain on asset sales	1,590	1,615
Operating and maintenance expenses (including affiliates)	7,380	8,414
Depreciation, depletion and amortization	6,762	10,016
Asset impairment	1,893
Interest expense, net	0	0
Net income (loss)	24,600	36,695
Total assets	1,016,827		1,047,922
Coal, Hard Mineral Royalty and Other | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	21
Soda Ash
Segment Reporting Information [Line Items]
Revenues	9,801	12,523
Soda Ash | Operating Segments
Segment Reporting Information [Line Items]
Revenues	9,801	12,523
Gain on asset sales	0	0
Operating and maintenance expenses (including affiliates)	0	0
Depreciation, depletion and amortization	0	0
Asset impairment	0
Interest expense, net	0	0
Net income (loss)	9,801	12,523
Total assets	258,939		261,942
Soda Ash | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	0
VantaCore
Segment Reporting Information [Line Items]
Revenues	24,682	26,799
VantaCore | Operating Segments
Segment Reporting Information [Line Items]
Revenues	24,682	26,799
Gain on asset sales	0	0
Operating and maintenance expenses (including affiliates)	22,156	25,434
Depreciation, depletion and amortization	3,562	3,856
Asset impairment	0
Interest expense, net	0	0
Net income (loss)	(1,036)	(2,491)
Total assets	196,720		200,348
VantaCore | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	(21)
Oil and Gas
Segment Reporting Information [Line Items]
Revenues	7,298	14,779
Oil and Gas | Operating Segments
Segment Reporting Information [Line Items]
Revenues	7,298	14,779
Gain on asset sales	20,335	451
Operating and maintenance expenses (including affiliates)	5,114	6,649
Depreciation, depletion and amortization	4,419	11,520
Asset impairment	137
Interest expense, net	0	0
Net income (loss)	17,963	$ (2,939)
Total assets	132,324		$ 158,862
Oil and Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	$ 0