Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Capital Surplus[Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2011	$ 311,134	$ 46,249	$ 103,335	$ 291,050	$ (125,593)	$ (3,907)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,049			28,049
Other comprehensive income (loss)	3,542					3,542
Acquisition of Virginia Savings Bancorp, Inc.	7,723		276		7,447
Cash dividends declared	(15,532)			(15,532)
Stock-based compensation expense, net	870		(179)		1,049
Exercise of stock options	544		(121)		665
Purchase of 237,535 treasury shares	(7,915)				(7,915)
Ending balance at Sep. 30, 2012	328,415	46,249	103,311	303,567	(124,347)	(365)
Beginning Balance at Dec. 31, 2012	333,274	46,249	103,524	309,270	(124,347)	(1,422)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,969			34,969
Other comprehensive income (loss)	(4,752)					(4,752)
Acquisition of Virginia Savings Bancorp, Inc.	28,508		4,236		24,272
Cash dividends declared	(17,686)			(17,686)
Stock-based compensation expense, net	963		(315)		1,278
Exercise of stock options	2,766		(170)		2,936
Ending balance at Sep. 30, 2013	$ 378,042	$ 46,249	$ 107,275	$ 326,553	$ (95,861)	$ (6,174)