Loans and Allowance for Loan Losses - Summary of Impaired Financial Receivables (Summary of Purchased Non-Covered Impaired Loans) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings not included above	$ 1,214,000	$ 3,390,000
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	18,249,000	6,659,000
Troubled debt restructurings not included above	1,212,000	5,938,000
Total impaired loans	19,461,000	12,597,000
Interest income recognized on impaired loans	109,000
Foregone interest income on impaired loans	$ 237,000