Hourglass Sands (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Operating costs and expenses		$ 62,419	$ 46,640
Cash and cash equivalents		8,690	$ 14,449		$ 15,502
Hourglass [Member]
Business Acquisition [Line Items]
Percentage of profit after capital investment and interest is returned				90.00%
Capitalization				$ 8,000
Cash and cash equivalents		2,300			2,900
Sand inventory		$ 1,600			$ 1,300
Hourglass [Member] | Director [Member]
Business Acquisition [Line Items]
Business acquisition purchase price	$ 4,000
Capital Unit, Class A [Member] | Hourglass [Member]
Business Acquisition [Line Items]
Percentage of profit until capital investment and interest is returned				100.00%
Hourglass Sands LLC [Member]
Business Acquisition [Line Items]
Date of acquisition agreement				Feb. 01, 2018
Business acquisition purchase price	$ 4,000
Hourglass Sands LLC [Member] | Hourglass [Member] | Director [Member]
Business Acquisition [Line Items]
Date of acquisition agreement				Feb. 01, 2018
Hourglass Sands LLC [Member] | Capital Unit, Class A [Member] | Hourglass [Member]
Business Acquisition [Line Items]
Equity method investment ownership percentage				100.00%