Loans - Summary of Impaired Financial Receivables (Summary of 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
Covered Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	38,359,000	59,781,000	35,412,000
Troubled debt restructurings not included above	20,721,000	22,775,000	22,619,000
Total impaired loans	59,080,000	82,556,000	58,031,000
Interest income recognized on impaired loans	220,000	387,000	2,057,000
Foregone interest income on impaired loans	$ 130,000	$ 10,000	$ 109,000