Loans - Summary of Impaired Financial Receivables (Summary of Covered Impaired Loans) (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings not included above	$ 14,000	$ 15,300	$ 21,100	$ 14,000	$ 21,100	$ 15,300
Covered Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income recognized on impaired loans	219	443	796	431	1,193	2,057
Foregone interest income on impaired loans	409	571	843	947	1,892	3,123
Nonaccrual loans	28,871	35,412	46,138	28,871	46,138	35,412
Troubled debt restructurings not included above	17,500	22,619	9,221	17,500	9,221	22,619
Total impaired loans	$ 46,371	$ 58,031	$ 55,359	$ 46,371	$ 55,359	$ 58,031