Acquisitions (Narrative) (Details) (USD $)	3 Months Ended				3 Months Ended		3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Virginia Savings Bank [Member]	May 31, 2012 Virginia Savings Bank [Member] item	Mar. 31, 2012 Community Bank [Member]	Jan. 10, 2013 Community Bank [Member]	Jan. 10, 2013 Community Bank [Member] Warrant [Member]	Jan. 10, 2013 Virginia Beach, Virginia [Member] Community Bank [Member] store	Mar. 31, 2013 Western Virginia [Member] Community Bank [Member] store
Business Acquisition [Line Items]
Percent of outstanding common and preferred stock						100.00%		100.00%
Number of branches acquired						5
Assets	$ 3,428,597,000	$ 2,917,466,000				$ 132,000,000		$ 460,000,000
Loans						82,000,000		410,000,000
Deposits	2,884,251,000	2,409,316,000				120,000,000		380,000,000
Shareholders equity	365,848,000	333,274,000	316,046,000	311,134,000		11,000,000		53,000,000
Transaction purchase price	53,840,000					12,395,000		41,445,000
Cash	17,410,000					4,672,000		12,738,000
Common stock value	35,506,000					7,723,000		27,783,000
Number of common stock shares issued						240,000		767,000	61,565
Exercise price per share									$ 30.80
Number of shares received by Community shareholders for each share of Community Financial	0.1753
Closing price of common stock at acquisition						$ 32.18		$ 36.23
Amortization time period for core deposit intangible assets	10 years
Core deposit annual charge, Maximum					700,000
Premium on time deposits						2,300,000		1,100,000
Premium on time deposits amortization period					5 years
Core deposit intangible	3,984,000					1,273,000		2,711,000
Goodwill	17,719,000					8,241,000		9,478,000
Number of branches										2	8
Transaction value								28,000,000
Merger related costs							$ 5,500,000