National Commerce Corporation (Parent Company Only) Financial Information - Statements of Cash Flows (Parenthetical) (Detail) (Parent Company [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Parent Company [Member]
     
Supplemental Cash Flow Information [Line Items]      
Proceeds from stock offering net of expenses $ 28 $ 28 $ 28