Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 21,152	$ 29,827
Accounts receivable, net	55,651	47,026
Accounts receivable—affiliates	94	161
Inventory	8,071	7,553
Prepaid expenses and other	3,088	5,838
Current assets of discontinued operations	991	991
Total current assets	89,047	91,396
Land	24,809	25,247
Plant and equipment, net	47,237	46,170
Mineral rights, net	878,845	883,885
Intangible assets, net	48,769	49,554
Equity in unconsolidated investment	241,679	245,433
Long-term contracts receivable	40,331	40,776
Other assets	6,489	6,547
Other assets—affiliate	0	156
Total assets	1,377,206	1,389,164
Current liabilities:
Accounts payable	5,911	6,957
Accounts payable—affiliates	2,093	562
Accrued liabilities	11,409	16,890
Accrued liabilities—affiliates	0	515
Accrued interest	5,706	15,484
Current portion of deferred revenue	1,554	0
Current portion of long-term debt, net	79,723	79,740
Current liabilities of discontinued operations	3	401
Total current liabilities	106,399	120,549
Deferred revenue	14,622	100,605
Long-term debt, net	724,854	729,608
Other non-current liabilities	2,492	2,808
Other non-current liabilities—affiliate	0	346
Total liabilities	848,367	953,916
Commitments and contingencies	0	0
Class A Convertible Preferred Units (250,000 and 258,844 units issued and outstanding at March 31, 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 March 31, 2018 and December 31, 2017, respectively)	301,344	199,851
General partner’s interest	3,924	1,857
Warrant holders’ interest	66,816	66,816
Accumulated other comprehensive loss	(4,438)	(3,313)
Total partners’ capital	367,646	265,211
Non-controlling interest	(3,394)	(3,394)
Total capital	364,252	261,817
Total liabilities and capital	$ 1,377,206	$ 1,389,164