Condensed Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue	$ 28,017	$ 28,435	$ 59,034	$ 58,710
Operating expenses:
Direct	10,996	11,939	23,904	24,439
Selling, general and administrative	7,940	6,905	15,808	13,591
Depreciation and amortization	1,325	1,139	2,608	2,244
Total operating expenses	20,261	19,983	42,320	40,274
Operating income	7,756	8,452	16,714	18,436
Other income (expense):
Interest income	9	15	54	29
Interest expense	(439)	(23)	(447)	(50)
Other, net	493	27	464	35
Total other income (expense)	63	19	71	14
Income before income taxes	7,819	8,471	16,785	18,450
Provision (benefit) for income taxes	(129)	2,719	1,531	6,178
Net income	7,948	5,752	15,254	12,272
Common Class A [Member]
Other income (expense):
Net income	$ 7,000	$ 2,855	$ 10,630	$ 6,088
Denominator for net income per share - basic:
Basic earnings per share (in dollars per share)	$ 0.29	$ 0.14	$ 0.47	$ 0.29
Numerator for net income per share - diluted:
Diluted earnings per share (in dollars per share)	0.28	0.13	0.45	0.28
Dividends Per Share of Common Stock:
Dividends per share (in dollars per share)	$ 0.17	$ 0.10	$ 0.27	$ 0.20
Weighted average shares and share equivalents outstanding:
Weighted average shares and share equivalents outstanding, basic (in shares)	23,957	20,752	22,429	20,745
Weighted average shares and share equivalents outstanding, diluted (in shares)	24,846	21,525	23,350	21,404
Common Class B [Member]
Other income (expense):
Net income	$ 948	$ 2,897	$ 4,624	$ 6,184
Denominator for net income per share - basic:
Basic earnings per share (in dollars per share)	$ 0.27	$ 0.82	$ 1.31	$ 1.75
Numerator for net income per share - diluted:
Diluted earnings per share (in dollars per share)	0.26	0.80	1.27	1.71
Dividends Per Share of Common Stock:
Dividends per share (in dollars per share)		$ 0.60	$ 0.60	$ 1.20
Weighted average shares and share equivalents outstanding:
Weighted average shares and share equivalents outstanding, basic (in shares)	3,527	3,514	3,527	3,514
Weighted average shares and share equivalents outstanding, diluted (in shares)	3,620	3,591	3,628	3,584