Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Class A [Member]
Other income (expense):
Net income	$ 8,759	$ 9,062	$ 7,741
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.42	$ 0.44	$ 0.37
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 0.41	$ 0.43	$ 0.37
Weighted average shares and share equivalents outstanding
Weighted average shares and share equivalents outstanding, basic (in shares)	20,741	20,764	20,677
Weighted average shares and share equivalents outstanding, diluted (in shares)	20,981	21,076	21,099
Common Class B [Member]
Other income (expense):
Net income	$ 8,851	$ 9,094	$ 7,743
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 2.52	$ 2.62	$ 2.25
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 2.49	$ 2.57	$ 2.20
Weighted average shares and share equivalents outstanding
Weighted average shares and share equivalents outstanding, basic (in shares)	3,478	3,473	3,447
Weighted average shares and share equivalents outstanding, diluted (in shares)	3,522	3,536	3,514
Revenue	$ 102,343	$ 98,837	$ 92,590
Direct	44,610	41,719	38,844
Selling, general and administrative	27,177	25,018	25,208
Depreciation, Depletion and Amortization, Nonproduction	4,109	3,804	3,732
Total operating expenses	75,896	70,541	67,784
Operating income	26,447	28,296	24,806
Interest income	60	83	63
Interest expense	(220)	(305)	(397)
Other, net	1,073	18	16
Total other expense	913	(204)	(318)
Income before income taxes	27,360	28,092	24,488
Provision for income taxes	9,750	9,936	9,004
Net income	$ 17,610	$ 18,156	$ 15,484