Loans and Allowance for Loan Losses - Schedule of Impaired Loans and Related Allowance (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