Loans - Summary of Impaired Financial Receivables Excluding Purchased Non-Covered and Covered 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
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income recognized on impaired loans	192	237	1,133	344	1,423	1,991
Foregone interest income on impaired loans	311	323	375	629	815	1,491
Nonaccrual loans	20,740	21,728	22,111	20,740	22,111	21,728
Troubled debt restructurings not included above	12,467	12,759	17,337	12,467	17,337	12,759
Total impaired loans	$ 33,207	$ 34,487	$ 39,448	$ 33,207	$ 39,448	$ 34,487