Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue	$ 119,686	$ 117,559	$ 109,384
Operating expenses:
Direct, exclusive of depreciation and amortization	47,577	49,068	45,577
Selling, general and administrative	31,371	29,686	28,385
Depreciation and amortization	5,463	4,586	4,225
Total operating expenses	84,411	83,340	78,187
Operating income	35,275	34,219	31,197
Other income (expense):
Interest income	62	96	47
Interest expense	(1,513)	(82)	(190)
Other, net	885	50	302
Total other income (expense)	(566)	64	159
Income before income taxes	34,709	34,283	31,356
Provision for income taxes	4,662	11,340	10,838
Net income	$ 30,047	$ 22,943	$ 20,518
Common Class A [Member]
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 1.08	$ 0.54	$ 0.49
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 1.04	$ 0.52	$ 0.48
Weighted average shares and share equivalents outstanding
Weighted average shares and share equivalents outstanding, basic (in shares)	23,562	20,770	20,713
Weighted average shares and share equivalents outstanding, diluted (in shares)	24,448	21,627	21,037
Common Class B [Member]
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 1.31	$ 3.26	$ 2.93
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 1.27	$ 3.18	$ 2.88
Weighted average shares and share equivalents outstanding
Weighted average shares and share equivalents outstanding, basic (in shares)	3,527	3,514	3,505
Weighted average shares and share equivalents outstanding, diluted (in shares)	3,628	3,603	3,560