Consolidated Statements Of Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Beginning balance at Dec. 31, 2011	$ 1,482,661	$ 31,163	$ 1,135,880	$ 375,184	$ 24,457	$ (84,023)
Beginning balance, shares at Dec. 31, 2011		31,163,070				1,789,165
Net income	19,393			19,393
Other comprehensive income (loss)	963				963
Cash dividends declared, $0.34 per share	(10,036)			(10,036)
Reissuance of treasury stock under incentive plan, net of shares surrendered in payment, including tax benefit	399		(489)			888
Reissuance of treasury stock under incentive plan, shares						(141,961)
Common stock issued for recognition and retention plan			(6,145)			6,145
Share-based compensation cost	2,250		2,250
Ending balance at Mar. 31, 2012	1,495,630	31,163	1,131,496	384,541	25,420	(76,990)
Ending balance, shares at Mar. 31, 2012		31,163,070				1,647,204
Beginning balance at Dec. 31, 2012	1,529,868	31,917	1,176,180	411,472	24,477	(114,178)
Beginning balance, shares at Dec. 31, 2012		31,917,385				2,427,640
Net income	717			717
Other comprehensive income (loss)	(1,185)				(1,185)
Cash dividends declared, $0.34 per share	(10,095)	0		(10,095)
Reissuance of treasury stock under incentive plan, net of shares surrendered in payment, including tax benefit	2,253		(1,193)			3,446
Reissuance of treasury stock under incentive plan, shares						(202,036)
Common stock issued for recognition and retention plan			(8,078)			8,078
Share-based compensation cost	2,512		2,512
Treasury stock acquired at cost
Ending balance at Mar. 31, 2013	$ 1,524,070	$ 31,917	$ 1,169,421	$ 402,094	$ 23,292	$ (102,654)
Ending balance, shares at Mar. 31, 2013		31,917,385				2,225,604