Junior Subordinated Debt - Junior Subordinated Debt Securities Outstanding (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Jul. 01, 2011
Debt Instrument [Line Items]
Principal Amount	$ 20,619
MidCarolina I [Member]
Debt Instrument [Line Items]
Valuation allowance associated with junior subordinated debenture	959		$ 1,197
MidCarolina II [Member]
Debt Instrument [Line Items]
Valuation allowance associated with junior subordinated debenture	827		$ 1,021
Junior Subordinated Debt Securities [Member]
Debt Instrument [Line Items]
Principal Amount	27,597	$ 27,521
Junior Subordinated Debt Securities [Member] | AMNB Trust I [Member]
Debt Instrument [Line Items]
Principal Amount	20,619	20,619
Junior Subordinated Debt Securities [Member] | MidCarolina I [Member]
Debt Instrument [Line Items]
Principal Amount	4,196	4,154
Junior Subordinated Debt Securities [Member] | MidCarolina II [Member]
Debt Instrument [Line Items]
Principal Amount	$ 2,782	$ 2,748
LIBOR [Member] | Junior Subordinated Debt Securities [Member] | AMNB Trust I [Member]
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.35%
LIBOR [Member] | Junior Subordinated Debt Securities [Member] | MidCarolina I [Member]
Debt Instrument [Line Items]
Basis Spread on Variable Rate	3.45%
LIBOR [Member] | Junior Subordinated Debt Securities [Member] | MidCarolina II [Member]
Debt Instrument [Line Items]
Basis Spread on Variable Rate	2.95%