Trust Preferred Capital Notes (Details) (USD $)	6 Months Ended								6 Months Ended		6 Months Ended		6 Months Ended				6 Months Ended	12 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 MidCarolina I [Member]	Jul. 01, 2011 MidCarolina I [Member]	Jun. 30, 2012 MidCarolina II [Member]	Jul. 01, 2011 MidCarolina II [Member]	Jul. 01, 2011 MidCarolina Trust [Member]	Jun. 30, 2012 Junior subordinated debt securities [Member]	Dec. 31, 2011 Junior subordinated debt securities [Member]	Jun. 30, 2012 Junior subordinated debt securities [Member] AMNB Trust I [Member]	Dec. 31, 2011 Junior subordinated debt securities [Member] AMNB Trust I [Member]	Jun. 30, 2012 Junior subordinated debt securities [Member] MidCarolina I [Member]	Dec. 31, 2011 Junior subordinated debt securities [Member] MidCarolina I [Member]	Jun. 30, 2012 Junior subordinated debt securities [Member] MidCarolina II [Member]	Dec. 31, 2011 Junior subordinated debt securities [Member] MidCarolina II [Member]	Jun. 30, 2012 AMNB Statutory Trust I [Member]	Jun. 30, 2012 MidCarolina Trust [Member]	Jun. 30, 2012 Trust preferred securities [Member]	Dec. 31, 2006 Trust preferred securities [Member]
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Proceeds from issuance of trust preferred securities																		$ 20,000,000
Maturity Date									Jun. 30, 2036		Nov. 07, 2032		Oct. 07, 2033				Jun. 30, 2036
Fixed interest rate of trust preferred securities (in hundredths)																	6.66%
Reference rate, trust preferred securities									Libor		Libor		Libor				three-month LIBOR
Trust preferred securities, basis spread on variable rate (in hundredths)									1.35%		3.45%		2.95%				1.35%
Number of consecutive quarterly periods for deferral of distributions on Trust Preferred Securities, Maximum																	20
Proceeds from issuance of common securities	619,000
Schedule of Equity Method Investments [Line Items]
Equity Method Investments															619,000	264,000
Debt Instrument [Line Items]
Date Issued									Apr. 07, 2006		Oct. 29, 2002		Dec. 03, 2003
Interest Rate									Libor plus 1.35%		Libor plus 3.45%		Libor plus 2.95%
Variable Rate Basis									Libor		Libor		Libor				three-month LIBOR
Basis Spread on Variable Rate (in hundredths)									1.35%		3.45%		2.95%				1.35%
Maturity Date									Jun. 30, 2036		Nov. 07, 2032		Oct. 07, 2033				Jun. 30, 2036
Principal Amount						8,764,000	27,267,000	27,212,000	20,619,000	20,619,000	4,014,000	3,986,000	2,634,000	2,607,000
Valuation allowance associated with junior subordinated debenture		$ 1,141,000	$ 1,197,000	$ 975,000	$ 1,021,000