Condensed Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Comprehensive Income
Balance at Dec. 31, 2009	$ 282,819	$ 31,849	$ 196,437	$ 59,915	$ (5,382)
Balance (in shares) at Dec. 31, 2009		12,739,533
Comprehensive income:
Net income	49,536			49,536		49,536
Change in net unrealized gain on securities available for sale, net of tax	6,153				6,153	6,153
Change in unrealized losses on derivative financial instruments qualifying as cash flow hedges, net of tax	(523)				(523)	(523)
Total comprehensive income	55,166					55,166
Cash dividends declared at $.34 per share	(4,336)			(4,336)
Employee stock purchases	142	13	129
Employee stock purchases (in shares)		5,294
Stock options exercised	226	30	196
Stock options exercised (in shares)		11,782
Restricted stock awards		57	(57)
Restricted stock awards (in shares)		22,698
Common stock repurchased	(198)	(14)	(184)
Common stock repurchased (in shares)		(5,452)
Share-based compensation expense	784		784
Balance at Jun. 30, 2010	334,603	31,935	197,305	105,115	248
Balance (in shares) at Jun. 30, 2010	12,773,855	12,773,855
Balance at Dec. 31, 2010	329,957	31,985	198,647	103,117	(3,792)
Balance (in shares) at Dec. 31, 2010	12,793,823	12,793,823
Comprehensive income:
Net income	7,434			7,434		7,434
Change in net unrealized gain on securities available for sale, net of tax	2,557				2,557	2,557
Change in unrealized losses on derivative financial instruments qualifying as cash flow hedges, net of tax	(68)				(68)	(68)
Total comprehensive income	9,923					9,923
Cash dividends declared at $.34 per share	(4,752)			(4,752)
Employee stock purchases	175	14	161
Employee stock purchases (in shares)		5,540
Stock options exercised	213	29	184
Stock options exercised (in shares)		11,550
Restricted stock awards		132	(132)
Restricted stock awards (in shares)		52,680
Common stock repurchased	(159)	(13)	(146)
Common stock repurchased (in shares)		(4,939)
Share-based compensation expense	909		909
Common stock issued in private placement offering	34,839	2,822	32,017
Common stock issued in private placement offering (in shares)		1,129,032
Balance at Jun. 30, 2011	$ 371,105	$ 34,969	$ 231,640	$ 105,799	$ (1,303)
Balance (in shares) at Jun. 30, 2011	13,987,686	13,987,686