Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts receivable, allowance for doubtful accounts	$ 381	$ 697
Property, plant and equipment, accumulated depreciation	139,045	136,753
Other intangible assets, amortization	$ 0	$ 2,184
Preferred stock, preferred stock authorized (in shares)	1,000,000.0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	25,000,000	25,000,000
Common stock, shares issued (in shares)	12,105,474	12,074,661
Treasury stock, shares (in shares)	5,864,244	5,864,641
Series A Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1
Preferred stock, Series A convertible shares authorized (in shares)	9,926
Preferred stock, Series A convertible shares issued (in shares)	9,926
Preferred stock, Series A convertible shares outstanding (in shares)	9,926