Loans, Leases and Allowance for Credit Losses - Summary of Recorded Investment in Nonaccrual Loans and Loans Past Due 90 Days Still Accruing Interest by Loan Class (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 27,459	$ 32,564
Total Non-accrual	36,868	43,925
Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,708	5,996
Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	330	1,156
Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	531	5,840
Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Construction and land development [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Construction and land development [Member] | Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	5,111
Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,557	14,083
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	333	378
Non-accrual loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	17,770	22,016
Total Non-accrual	36,868	43,925
Non-accrual loans [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,083	4,113
Total Non-accrual	23,977	22,026
Non-accrual loans [Member] | Commercial real estate [Member] | Owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	792
Total Non-accrual	0	1,881
Non-accrual loans [Member] | Commercial real estate [Member] | Non-owner occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	5,840
Total Non-accrual	0	5,840
Non-accrual loans [Member] | Commercial real estate [Member] | Multi-family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Total Non-accrual	0	0
Non-accrual loans [Member] | Construction and land development [Member] | Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Total Non-accrual	0	0
Non-accrual loans [Member] | Construction and land development [Member] | Land [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	5,111
Total Non-accrual	0	5,979
Non-accrual loans [Member] | Residential real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,354	6,078
Total Non-accrual	12,558	8,117
Non-accrual loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	333	82
Total Non-accrual	$ 333	$ 82