Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts	$ 430	$ 697
Accumulated amortization	$ 0	$ 2,184
Preferred stock, shares authorized (in shares)	1,000,000
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)	12,115,055	12,074,661
Treasury stock, shares (in shares)	5,854,980	5,864,641
Series A Convertible Preferred Stock
Preferred stock, par value (in dollars per share)	$ 1
Preferred stock, shares authorized (in shares)	9,926
Preferred stock, shares issued (in shares)	9,926
Preferred stock, shares outstanding (in shares)	9,926