Segment Reporting - Schedule of Reconciliation of Reportable Segment Revenue, Expenses and Profit (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]          
Interest income $ 12,714 $ 6,449 $ 24,907 $ 12,657  
Interest expense 1,071 634 2,098 1,293  
Net interest income 11,643 5,815 22,809 11,364  
Provision for loan and lease losses 120   281    
Noninterest income 2,206 1,326 3,970 2,293  
Noninterest expense 9,616 5,435 18,906 10,316  
Earnings before income taxes 4,113 1,706 7,592 3,341  
Income tax expense 1,264 568 2,356 1,160  
Noncontrolling interest (593)   (1,059)    
Net earnings attributable to National Commerce Corporation 2,256 1,138 4,177 2,181  
Total assets 1,256,614 783,197 1,256,614 783,197 $ 1,138,426
Operating Segments [Member] | Retail and Commercial Banking [Member]          
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]          
Interest income 10,051 6,328 19,566 12,466  
Interest expense 1,034 599 2,032 1,238  
Net interest income 9,017 5,729 17,534 11,228  
Provision for loan and lease losses 428   429    
Noninterest income 377 166 924 324  
Noninterest expense 6,873 4,471 13,789 8,583  
Earnings before income taxes 2,093 1,424 4,240 2,969  
Income tax expense 721 461 1,485 1,019  
Net earnings attributable to National Commerce Corporation 1,372 963 2,755 1,950  
Total assets 1,213,137 771,275 1,213,137 771,275  
Operating Segments [Member] | Mortgage Division [Member]          
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]          
Interest income 113 121 197 191  
Interest expense 37 35 66 55  
Net interest income 76 86 131 136  
Noninterest income 1,829 1,160 3,017 1,969  
Noninterest expense 1,453 964 2,493 1,733  
Earnings before income taxes 452 282 655 372  
Income tax expense 172 107 249 141  
Net earnings attributable to National Commerce Corporation 280 175 406 231  
Total assets 13,750 $ 11,922 13,750 $ 11,922  
Operating Segments [Member] | Receivables Factoring [Member]          
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]          
Interest income 3,048   6,161    
Interest expense 498   1,017    
Net interest income 2,550   5,144    
Provision for loan and lease losses (308)   (148)    
Noninterest income     29    
Noninterest expense 1,290   2,624    
Earnings before income taxes 1,568   2,697    
Income tax expense 371   622    
Noncontrolling interest (593)   (1,059)    
Net earnings attributable to National Commerce Corporation 604   1,016    
Total assets 97,687   97,687    
Elimination Entries [Member]          
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]          
Interest income (498)   (1,017)    
Interest expense (498)   (1,017)    
Total assets $ (67,960)   $ (67,960)