Unaudited Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities
Net cash provided by (used for) operating activities	$ 29,318	$ (12,489)
Investing activities
Expenditures for property, plant and equipment and acquisition of mineral interests	(16,127)	(12,799)
Proceeds from the sale of property, plant and equipment	59	550
Purchase of equity securities	0	(2,000)
Other	(21)	(395)
Net cash used for investing activities	(16,089)	(14,644)
Financing activities
Additions to long-term debt	0	6,302
Reductions of long-term debt	(2,881)	(823)
Net reductions to revolving credit agreements	(11,000)	(2,000)
Cash dividends paid	(2,786)	(2,690)
Purchase of treasury shares	0	(1,002)
Net cash used for financing activities	(16,667)	(213)
Cash and cash equivalents
Total decrease for the period	(3,438)	(27,346)
Balance at the beginning of the period	88,450	122,892
Balance at the end of the period	$ 85,012	$ 95,546