Junior Subordinated Debt - Additional Information (Details) $ in Thousands	Sep. 30, 2011	Apr. 07, 2006 USD ($)	Sep. 30, 2017 USD ($)	Jul. 01, 2011 USD ($) trust
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Proceeds from issuance of trust preferred securities		$ 20,000
Number of consecutive quarterly periods (up to 20 quarterly periods)	5 years
Proceeds from issuance of common securities		619
Junior subordinated debt securities, amount		$ 20,619
MidCarolina | Delaware
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Number of statutory trusts | trust				2
Mid Carolina Trust
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Junior subordinated debt securities, amount				$ 8,764
Equity method investments			$ 264
AMNB Trust I
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Equity method investments			$ 619