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Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Income Taxes [Line Items]                        
Federal income tax rate                   35.00% 35.00% 35.00%
State net operating loss carryforward $ 9,700       $ 1,200         $ 9,700 $ 1,200  
State net operating loss carryforwards expiration period                   2030    
Deferred tax asset for the allowance for credit losses 5,000                 $ 5,000    
Deferred tax assets, state taxes 300       32         300 32  
Income tax expense 923 $ 3,235 $ 3,751 $ 2,385 $ 4,014 $ 4,020 $ 3,668 $ 3,215   10,294 14,917 $ 14,774
Tax benefit                   1,600 $ 0 $ 0
Provisional benefit to income tax expense, Tax Act $ 3,100                 $ 3,122    
Tax Year 2013 [Member] | Tennessee [Member]                        
Schedule Of Income Taxes [Line Items]                        
Open tax year                   2013    
Tax Year 2013 [Member] | South Carolina [Member]                        
Schedule Of Income Taxes [Line Items]                        
Open tax year                   2013    
Earliest Tax Year [Member] | Texas [Member]                        
Schedule Of Income Taxes [Line Items]                        
Open tax year                   2011    
Scenario, Forecast [Member]                        
Schedule Of Income Taxes [Line Items]                        
Federal income tax rate                 21.00%