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 ($)	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Carrying amount of purchased credit impaired loans	$ 1,970,000	$ 2,178,000	$ 2,037,000
Troubled debt restructured loans	973,000	199,000	177,000
Doubtful [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Troubled debt restructured loans	$ 8,527,000	$ 6,113,000	$ 8,431,000