Loans - Summary of Impaired Financial Receivables (Summary of Purchased Non-Covered Impaired Loans) (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings not included above	$ 1,519,000	$ 2,241,000	$ 1,212,000
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	17,308,000	15,318,000	18,249,000
Troubled debt restructurings not included above	1,526,000	5,191,000	1,212,000
Total impaired loans	18,834,000	20,509,000	19,461,000
Interest income recognized on impaired loans	18,000	74,000	360,000
Foregone interest income on impaired loans	$ 21,000	$ 563,000	$ 237,000