Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 63,387	$ 29,827
Accounts receivable, net	55,734	47,026
Accounts receivable—affiliates	22	161
Inventory	9,572	7,553
Prepaid expenses and other	4,665	5,838
Current assets of discontinued operations	988	991
Total current assets	134,368	91,396
Land	24,809	25,247
Plant and equipment, net	48,148	46,170
Mineral rights, net	869,106	883,885
Intangible assets, net	46,998	49,554
Equity in unconsolidated investment	242,901	245,433
Long-term contracts receivable	39,416	40,776
Other assets	6,188	6,547
Other assets—affiliate	0	156
Total assets	1,411,934	1,389,164
Current liabilities:
Accounts payable	7,467	6,957
Accounts payable—affiliates	608	562
Accrued liabilities	14,005	16,890
Accrued liabilities—affiliates	0	515
Accrued interest	5,540	15,484
Current portion of deferred revenue	1,403	0
Current portion of long-term debt, net	75,201	79,740
Current liabilities of discontinued operations	0	401
Total current liabilities	104,224	120,549
Deferred revenue	40,885	100,605
Long-term debt, net	716,514	729,608
Other non-current liabilities	1,958	2,808
Other non-current liabilities—affiliate	0	346
Total liabilities	863,581	953,916
Commitments and contingencies	0	0
Class A Convertible Preferred Units (250,000 and 258,844 units issued and outstanding at September 30, 2018 and December 31, 2017, respectively, at $1,000 par value per unit; liquidation preference of $1,500 per unit)	164,587	173,431
Partners’ capital:
Common unitholders’ interest (12,245,920 and 12,232,006 units issued and outstanding at September 30, 2018 and December 31, 2017, respectively)	319,673	199,851
General partner’s interest	4,293	1,857
Warrant holders’ interest	66,816	66,816
Accumulated other comprehensive loss	(4,081)	(3,313)
Total partners’ capital	386,701	265,211
Non-controlling interest	(2,935)	(3,394)
Total capital	383,766	261,817
Total liabilities and capital	$ 1,411,934	$ 1,389,164