Acquisitions (Narrative) (Details) (USD $)	9 Months Ended					9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2012 Community Bank [Member]	Sep. 30, 2012 Virginia Savings Bank [Member]	May 31, 2012 Virginia Savings Bank [Member] item	Sep. 30, 2012 Virginia Beach, Virginia [Member] Community Bank [Member]	Sep. 30, 2012 Western Virginia [Member] Community Bank [Member]
Business Acquisition [Line Items]
Percent of outstanding common and preferred stock							100.00%
Number of branches acquired							5
Assets	$ 2,899,197,000	$ 2,777,109,000			$ 500,000,000		$ 132,000,000
Loans							82,000,000
Deposits	2,381,496,000	2,221,268,000					120,000,000
Shareholders equity	328,415,000	311,134,000	309,892,000	314,861,000			11,000,000
Transaction purchase price							12,395,000
Cash							4,672,000
Common stock value							7,723,000
Number of common stock shares acquired							240,000
Closing price of common stock at acquisition							$ 32.18
Amortization time period for core deposit intangible assets	10 years
Core deposit annual charge, Maximum						200,000
Premium on time deposits						2,300,000
Premium on time deposits amortization period						5 years
Core deposit intangible							1,273,000
Number of branches								2	8
Transaction value					$ 26,600,000