Consolidated Statements of Stockholders' Equity (USD $)	Total	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock	Common Class A [Member]	Common Class B [Member]
Beginning balance at Dec. 31, 2008	$ 363,583,865	$ 163,136,938	$ 1,713,836	$ 207,182,253	$ (8,710,602)	$ 204,948	$ 56,492
Beginning balance, shares at Dec. 31, 2008						20,494,764	5,649,240
Issuance of common stock (stock compensation plans)	1,386,037	1,385,285				752
Issuance of common stock (stock compensation plans), shares						75,166
Net income	18,830,078			18,830,078
Cash dividends	(11,193,845)			(11,193,845)
Grant of stock options		62,991		(62,991)
Purchase of treasury stock	(393,644)				(393,644)
Other comprehensive income (loss)	13,293,208		13,293,208
Ending balance at Dec. 31, 2009	385,505,699	164,585,214	15,007,044	214,755,495	(9,104,246)	205,700	56,492
Ending balance, shares at Dec. 31, 2009						20,569,930	5,649,240
Issuance of common stock (stock compensation plans)	1,199,422	1,198,556				866
Issuance of common stock (stock compensation plans), shares						86,597
Net income	11,467,179			11,467,179
Cash dividends	(11,477,845)			(11,477,845)
Grant of stock options		1,309,734		(1,309,734)
Purchase of treasury stock	(145,687)				(145,687)
Other comprehensive income (loss)	(6,445,958)		(6,445,958)
Ending balance at Dec. 31, 2010	380,102,810	167,093,504	8,561,086	213,435,095	(9,249,933)	206,566	56,492
Ending balance, shares at Dec. 31, 2010						20,656,527	5,649,240
Issuance of common stock (stock compensation plans)	1,460,543	1,459,579				964
Issuance of common stock (stock compensation plans), shares						96,472
Net income	452,953			452,953
Cash dividends	(11,999,488)			(11,999,488)
Grant of stock options		2,283,860		(2,283,860)
Purchase of treasury stock	(1,537,587)				(1,537,587)
Other comprehensive income (loss)	14,972,361		14,972,361
Ending balance at Dec. 31, 2011	$ 383,451,592	$ 170,836,943	$ 23,533,447	$ 199,604,700	$ (10,787,520)	$ 207,530	$ 56,492
Ending balance, shares at Dec. 31, 2011						20,752,999	5,649,240