Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Deferred Compensation [Member]	Accumulated Other Comprehensive Earnings [Member]	Total
Balance at Dec. 31, 2009	$ 208	$ 269,294	$ 115,123	$ (3,833)	$ 3,833	$ 31,077	$ 415,702
Balance, shares at Dec. 31, 2009	20,826,431			(162,836)
Net earnings (unaudited)			27,915				27,915
Stock issuances (unaudited)		569					569
Stock issuances (unaudited), shares	21,990
Cash dividends declared $0.45 and $0.24 for six months ended June 30, 2010 and 2011 respectively, per share (unaudited)			(14,175)				(14,175)
Change in unrealized gain in investment securities available-for-sale, net of related income taxes (unaudited)						763	763
Additional tax benefit related to directors' deferred compensation plan (unaudited)		30					30
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)				(205)	205
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), shares				(2,129)
Stock option expense (unaudited)		194					194
Balance at Jun. 30, 2010	208	270,087	128,863	(4,038)	4,038	31,840	430,998
Balance, shares at Jun. 30, 2010	20,848,421			(164,965)
Balance at Dec. 31, 2010	209	274,629	146,397	(4,207)	4,207	20,453	441,688
Balance, shares at Dec. 31, 2010	20,942,141			(166,329)
Net earnings (unaudited)			32,815				32,815
Stock issuances (unaudited)		804					804
Stock issuances (unaudited), shares	27,982
Cash dividends declared $0.45 and $0.24 for six months ended June 30, 2010 and 2011 respectively, per share (unaudited)			(14,690)				(14,690)
Change in unrealized gain in investment securities available-for-sale, net of related income taxes (unaudited)						16,851	16,851
Additional tax benefit related to directors' deferred compensation plan (unaudited)		20					20
Shares purchased in connection with directors' deferred compensation plan, net (unaudited)				(187)	187
Shares purchased in connection with directors' deferred compensation plan, net (unaudited), shares				(2,041)
Stock option expense (unaudited)		217					217
Three-for-two stock split in the form of a 50% stock dividend (unaudited)	105		(105)
Three-for-two stock split in the form of a 50% stock dividend (unaudited), shares	10,481,177			(83,146)
Balance at Jun. 30, 2011	$ 314	$ 275,670	$ 164,417	$ (4,394)	$ 4,394	$ 37,304	$ 477,705
Balance, shares at Jun. 30, 2011	31,451,300			(251,516)