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 $)	0 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Receivables [Abstract]
Carrying amount of purchased credit impaired loans	$ 2,037,000	$ 2,151,000	$ 2,037,000	$ 2,605,000	$ 2,151,000
Troubled debt restructured loans			$ 8,431,000	$ 11,449,000	$ 9,073,000