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, 2015	Dec. 31, 2014	Sep. 30, 2014
Receivables [Abstract]
Carrying amount of purchased credit impaired loans	$ 2,422,000	$ 2,151,000	$ 2,383,000
Troubled debt restructured loans	$ 6,462,000	$ 9,073,000	$ 10,114,000