Loans and Allowance for Loan Losses - Summary of Impaired Financial Receivables (Summary of Covered Impaired Loans) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings not included above	$ 1,214,000	$ 3,390,000
Covered Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	35,412,000	69,152,000	115,712,000
Troubled debt restructurings not included above	22,619,000	22,243,000	17,090,000
Total impaired loans	58,031,000	91,395,000	132,802,000
Interest income recognized on impaired loans	1,134,000	968,000	849,000
Foregone interest income on impaired loans	$ 109,000	$ 330,000	$ 491,000