Consolidated Statements of Stockholders' Equity (USD $)	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)
Balance at Dec. 31, 2009	$ 25,982,383	$ 517,002	$ 114,021	$ 24,690,293	$ 661,067
Balance (in shares) at Dec. 31, 2009		5,170,018
Increase (Decrease) in Stockholders' Equity
Stock options exercised, net of surrendered shares	454,124	9,562	444,562
Stock options exercised, net of surrendered shares (in shares)		95,618
Dividends declared ($0.42, $0.40 and $0.38 per share for the year ended December 31, 2012, 2011 and 2010, respectively)	(1,987,806)			(1,987,806)
Stock-based compensation expense	261,859		261,859
Tax benefit on stock plans	101,830		101,830
Net income	4,518,384			4,518,384
Cumulative translation adjustment	(922,163)				(922,163)
Balance at Dec. 31, 2010	28,408,611	526,564	922,272	27,220,871	(261,096)
Balance (in shares) at Dec. 31, 2010		5,265,636
Increase (Decrease) in Stockholders' Equity
Stock options exercised, net of surrendered shares	1,260,598	17,317	1,243,281
Stock options exercised, net of surrendered shares (in shares)		173,174
Dividends declared ($0.42, $0.40 and $0.38 per share for the year ended December 31, 2012, 2011 and 2010, respectively)	(2,148,384)			(2,148,384)
Stock-based compensation expense	388,904		388,904
Tax benefit on stock plans	208,067		208,067
Net income	5,450,918			5,450,918
Cumulative translation adjustment	(328,935)				(328,935)
Balance at Dec. 31, 2011	33,239,779	543,881	2,762,524	30,523,405	(590,031)
Balance (in shares) at Dec. 31, 2011	5,438,810	5,438,810
Increase (Decrease) in Stockholders' Equity
Stock options exercised, net of surrendered shares	421,680	7,916	413,764
Stock options exercised, net of surrendered shares (in shares)		79,156
Dividends declared ($0.42, $0.40 and $0.38 per share for the year ended December 31, 2012, 2011 and 2010, respectively)	(2,307,402)			(2,307,402)
Stock-based compensation expense	464,470		464,470
Tax benefit on stock plans	98,210		98,210
Net income	2,001,974			2,001,974
Cumulative translation adjustment	(37,263)				(37,263)
Balance at Dec. 31, 2012	$ 33,881,448	$ 551,797	$ 3,738,968	$ 30,217,977	$ (627,294)
Balance (in shares) at Dec. 31, 2012	5,517,966	5,517,966