Consolidated Statement of Stockholders' Equity (USD $)	Total	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Common Class A [Member]	Common Class B [Member]
Beginning balance at Dec. 31, 2012	$ 400,034,094	$ 176,416,585	$ 26,394,577	$ 209,670,214	$ (12,713,193)	$ 209,419	$ 56,492
Beginning balance, shares at Dec. 31, 2012						20,941,821	5,649,240
Issuance of common stock (stock compensation plans)	6,058,319	6,054,128				4,191
Issuance of common stock (stock compensation plans), shares						419,171
Net income	16,758,157			16,758,157
Cash dividends declared	(6,466,257)			(6,466,257)
Grant of stock options		47,995		(47,995)
Tax benefit on exercise of stock options	208,867	208,867
Repurchase of treasury shares	(60,024)				(60,024)
Other comprehensive loss	(27,454,476)		(27,454,476)
Ending balance at Sep. 30, 2013	$ 389,078,680	$ 182,727,575	$ (1,059,899)	$ 219,914,119	$ (12,773,217)	$ 213,610	$ 56,492
Ending balance, shares at Sep. 30, 2013						21,360,992	5,649,240