CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY - USD ($)	Additional paid-in capital [Member]	Retained earnings [Member]	Treasury stock [Member]	Accumulated other comprehensive loss [Member]	Common Class A [Member]	Total
Balance at Dec. 31, 2017	$ 13,064,000	$ 34,455,000	$ (5,179,000)	$ (530,000)	$ 4,203,000	$ 46,013,000
Balance (in shares) at Dec. 31, 2017			(631,000)		4,203,000
Net income	0	370,000	$ 0	0	$ 0	370,000
Exercise of stock options	553,000	0	0	0	$ 184,000	737,000
Exercise of stock options (in shares)					184,000
Restricted common stock compensation	11,000	0	0	0	$ 7,000	18,000
Restricted common stock compensation (in shares)					7,000
Purchase of Class A common stock	0	0	$ (430,000)	0	$ 0	(430,000)
Purchase of Class A common stock (in shares)			(52,000)
Stock-based compensation	120,000	0	$ 0	0	0	120,000
Dividends	0	(359,000)	0	0	0	(359,000)
Foreign currency translation adjustment	0	0	0	(59,000)	0	(59,000)
Balance at Jun. 30, 2018	13,748,000	34,466,000	$ (5,609,000)	(589,000)	$ 4,394,000	46,410,000
Balance (in shares) at Jun. 30, 2018			(683,000)		4,394,000
Balance at Mar. 31, 2018	13,210,000	34,340,000	$ (5,261,000)	(434,000)	$ 4,229,000	46,084,000
Balance (in shares) at Mar. 31, 2018			(641,000)		4,229,000
Net income	0	305,000	$ 0	0	$ 0	305,000
Exercise of stock options	474,000	0	0	0	$ 158,000	632,000
Exercise of stock options (in shares)					158,000
Restricted common stock compensation	4,000	0	0	0	$ 7,000	11,000
Restricted common stock compensation (in shares)					7,000
Purchase of Class A common stock	0	0	$ (348,000)	0	$ 0	(348,000)
Purchase of Class A common stock (in shares)			(42,000)
Stock-based compensation	60,000	0	$ 0	0	0	60,000
Dividends	0	(179,000)	0	0	0	(179,000)
Foreign currency translation adjustment	0	0	0	(155,000)	0	(155,000)
Balance at Jun. 30, 2018	13,748,000	34,466,000	$ (5,609,000)	(589,000)	$ 4,394,000	46,410,000
Balance (in shares) at Jun. 30, 2018			(683,000)		4,394,000
Balance at Dec. 31, 2018	13,904,000	34,588,000	$ (6,695,000)	(672,000)	$ 4,410,000	45,535,000
Balance (in shares) at Dec. 31, 2018			(816,000)		4,410,000
Net income	0	5,662,000	$ 0	0	$ 0	5,662,000
Restricted common stock compensation	20,000	0	0	0	$ 6,000	26,000
Restricted common stock compensation (in shares)					6,000
Purchase of Class A common stock	0	0	$ (3,467,000)	0	$ 0	(3,467,000)
Purchase of Class A common stock (in shares)			(450,000)
Stock-based compensation	62,000	0	$ 0	0	0	62,000
Dividends	0	(317,000)	0	0	0	(317,000)
Foreign currency translation adjustment	0	0	0	(7,000)	0	(7,000)
Balance at Jun. 30, 2019	13,986,000	39,933,000	$ (10,162,000)	(679,000)	$ 4,416,000	47,494,000
Balance (in shares) at Jun. 30, 2019			(1,266,000)		4,416,000
Balance at Mar. 31, 2019	13,946,000	34,404,000	$ (9,897,000)	(628,000)	$ 4,410,000	42,235,000
Balance (in shares) at Mar. 31, 2019			(1,234,000)		4,410,000
Net income	0	5,688,000	$ 0	0	$ 0	5,688,000
Restricted common stock compensation	7,000	0	0	0	$ 6,000	13,000
Restricted common stock compensation (in shares)					6,000
Purchase of Class A common stock	0	0	$ (265,000)	0	$ 0	(265,000)
Purchase of Class A common stock (in shares)			(32,000)
Stock-based compensation	33,000	0	$ 0	0	0	33,000
Dividends	0	(159,000)	0	0	0	(159,000)
Foreign currency translation adjustment	0	0	0	(51,000)	0	(51,000)
Balance at Jun. 30, 2019	$ 13,986,000	$ 39,933,000	$ (10,162,000)	$ (679,000)	$ 4,416,000	$ 47,494,000
Balance (in shares) at Jun. 30, 2019			(1,266,000)		4,416,000