Loans and Allowance for Loan Losses - Non-Accrual Loans, Loans Still Accruing and Past Due 90 Days or More and Restructured Loans (Parenthetical) (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	$ 33,712,000	$ 28,601,000	$ 21,788,000
Troubled debt restructured loans	750,000	199,000	204,000
Purchased Credit Impaired Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Non-accrual loans	1,853,000	2,178,000	2,422,000
Doubtful [Member]
Loans and Leases Receivable Disclosure [Line Items]
Troubled debt restructured loans	$ 7,513,000	$ 6,113,000	$ 6,462,000