Consolidated Balance Sheets (Parenthetical) $ in Thousands	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Statement of Financial Position [Abstract]
Allowances for account receivable | $	$ 1,523	$ 1,523
Class A Common Stock
Common stock, par value (in usd per share) | $ / shares	$ 1	$ 1
Common stock, shares outstanding (in shares) | shares	5,282,106	5,207,955
Class B Common Stock
Common stock, par value (in usd per share) | $ / shares	$ 1	$ 1
Common stock, shares outstanding (in shares) | shares	1,570,146	1,570,915
Common stock, convertible conversion ratio	1	1