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Fair Value Measurement of Assets and Liabilities - Additional Information (Detail)
$ in Thousands
12 Months Ended
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Security
Dec. 31, 2015
USD ($)
Dec. 31, 2017
security
Dec. 31, 2017
Security
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Collateral dependent loan charge-offs $ 2,100 $ 4,300      
Collateral dependent impaired loans, recorded investment 57,500 8,400      
Specific valuation allowance allocations 9,100 3,000      
Reported net carrying amount of impaired loans $ 48,400 5,400      
Valuation of loan servicing rights, discount rate 8.00%        
Net impairment (recovery of impairment) on loan servicing rights $ 429 611      
Foreclosed assets measured at fair value upon initial recognition 3,500 4,500      
Allowance for loan losses, charge-offs 1,900 1,700      
Loss due to re-measurement of repossessed assets $ 361 $ 1,000 $ 2,000    
Minimum          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Valuation of loan servicing rights, prepayment rate 0.00%        
Maximum          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Valuation of loan servicing rights, prepayment rate 22.00%        
Trust preferred securities          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Number of available for sale securities   2   1 1
Significant Unobservable Inputs (Level 3) | Residential mortgage-backed securities          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Number of available for sale securities | security       4  
Significant Unobservable Inputs (Level 3) | Trust preferred securities          
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]          
Number of available for sale securities | security       1