Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Thousands
 3 Months Ended 12 Months Ended
Sep. 30, 2016
USD ($)
Dec. 31, 2017
USD ($)
branch
loan_pool
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Proceeds from redemption of FRB stock | $ $ 14,400 $ 0 $ 14,423 $ 0
Allowance for loan losses of loans receivable | $   $ 31,043 $ 32,429  
Estimated loss emergence period   2 years 6 months 2 years 6 months 1 year
General loan pools [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Number of loan pools | loan_pool   14    
Nonperforming Financing Receivable [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Delinquency period of loans with respect to interest or principal for discontinuance of accrual of interest income (less than)   90 days    
Cash and Cash Equivalents [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Delinquency period of loans with respect to interest or principal for discontinuance of accrual of interest income (less than)   90 days    
Full Service [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Number of branches | branch   40    
Loan Production [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Number of branches | branch   8    
Equipment Financing Receivable [Member] | Minimum [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Intangible asset amortization period   1 year    
Equipment Financing Receivable [Member] | Maximum [Member]        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Intangible asset amortization period   7 years