Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue	$ 109,384	$ 102,343	$ 98,837
Operating expenses:
Direct	45,577	44,610	41,719
Selling, general and administrative	28,385	27,177	25,018
Depreciation and amortization	4,225	4,109	3,804
Total operating expenses	78,187	75,896	70,541
Operating income	31,197	26,447	28,296
Other income (expense):
Interest income	47	60	83
Interest expense	(190)	(220)	(305)
Other, net	302	1,073	18
Total other expense	159	913	(204)
Income before income taxes	31,356	27,360	28,092
Provision for income taxes	10,838	9,750	9,936
Net income	20,518	17,610	18,156
Common Class A [Member]
Other income (expense):
Net income	$ 10,178	$ 8,759	$ 9,062
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.49	$ 0.42	$ 0.44
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 0.48	$ 0.41	$ 0.43
Weighted average shares and share equivalents outstanding
Weighted average shares and share equivalents outstanding, basic (in shares)	20,713	20,741	20,764
Weighted average shares and share equivalents outstanding, diluted (in shares)	21,037	20,981	21,076
Common Class B [Member]
Other income (expense):
Net income	$ 10,341	$ 8,851	$ 9,094
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 2.93	$ 2.52	$ 2.62
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 2.88	$ 2.49	$ 2.57
Weighted average shares and share equivalents outstanding
Weighted average shares and share equivalents outstanding, basic (in shares)	3,505	3,478	3,473
Weighted average shares and share equivalents outstanding, diluted (in shares)	3,560	3,522	3,536