Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Accounts receivable, net of allowances of $477 and $432, respectively	$ 477	$ 432
Property, plant and equipment, net of accumulated depreciation of $155,718 and $154,939, respectively	155,718	154,939
Accumulated amortization on intangible assets	$ 12,099	$ 11,440
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
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued (in shares)	30,847,269	30,801,255
Common stock, shares outstanding (in shares)	30,847,269	30,801,255
Treasury stock, shares (in shares)	1,334,251	1,334,251