Quarterly report pursuant to Section 13 or 15(d)

Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail)

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Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Loss Contingencies [Line Items]          
Total undisbursed loan commitments $ 327,403   $ 327,403   $ 330,871
Allowance for Loan Off-Balance Sheet Items [Roll Forward]          
Balance at beginning of period     32,429    
Loan and lease loss provision (income) 269 $ (1,450) 611 $ (4,490)  
Balance at end of period 32,492   32,492    
Non-PCI Loans and Leases [Member]          
Allowance for Loan Off-Balance Sheet Items [Roll Forward]          
Balance at beginning of period 33,038 34,259 31,458 37,494  
Loan and lease loss provision (income) 194 (1,540) 787 (4,724)  
Balance at end of period 31,698 33,439 31,698 33,439  
Allowance for off-balance sheet items [Member] | Non-PCI Loans and Leases [Member]          
Allowance for Loan Off-Balance Sheet Items [Roll Forward]          
Balance at beginning of period 1,135 1,475 1,184 986  
Loan and lease loss provision (income) (220) 16 (269) 505  
Balance at end of period 915 $ 1,491 915 $ 1,491  
Commitments to extend credit [Member]          
Loss Contingencies [Line Items]          
Total undisbursed loan commitments 301,049   301,049   310,987
Standby letters of credit [Member]          
Loss Contingencies [Line Items]          
Total undisbursed loan commitments 19,521   19,521   15,669
Commercial letters of credit [Member]          
Loss Contingencies [Line Items]          
Total undisbursed loan commitments $ 6,833   $ 6,833   $ 4,215