Loans and Allowance for Loan Losses - Summary of Nonperforming and Restructured Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Summary Of Nonperforming And Restructured Assets [Abstract]
Past due 90 days or more and still accruing	$ 1,135	$ 1,179
Nonaccrual	16,410	14,390
Restructured	16,515	17,624
Total nonperforming and restructured loans	34,060	33,193
Other real estate owned and repossessed assets	8,079	8,386
Total nonperforming and restructured assets	$ 42,139	$ 41,579
Nonperforming and restructured loans to total loans	0.88%	0.98%
Nonperforming and restructured assets to total assets	0.64%	0.69%