Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Allowance for accounts receivable	$ 727	$ 518
Accumulated amortization on other intangibles, deferred costs and investments	$ 12,588	$ 11,804
Preferred Stock, Shares Authorized	1,500	1,500
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Treasury stock, shares (in shares)	1,656	1,625
Class A Common Stock [Member]
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, Shares Authorized	35,000	35,000
Common Stock, Shares, Issued	6,694	6,638
Class B Common Stock [Member]
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, Shares Authorized	3,500	3,500
Common Stock, Shares, Issued	898	878
Common Stock, Shares, Outstanding	898	878