CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - Parenthetical - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,213	$ 0
Property, plant and equipment, accumulated amortization, depreciation and amortization	349,444	314,276
Owned and lease mineral rights, accumulated depletion and amortization	33,590	27,877
Other acquired intangibles, accumulated amortization	$ 34,631	$ 32,686
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	20,500,000.0	20,500,000.0
Common stock, shares outstanding (in shares)	18,300,000.0	18,200,000.0
Treasury stock, shares at cost (in shares)	2,300,000.0	2,300,000.0