Loans and Allowance for Loan Losses - Summary of Nonperforming and Restructured Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Summary Of Nonperforming And Restructured Assets [Abstract]
Past due 90 days or more and still accruing	$ 2,893	$ 1,962
Nonaccrual	31,943	31,798
Restructured	4,720	1,713
Total nonperforming and restructured loans	39,556	35,473
Other real estate owned and repossessed assets	4,424	3,866
Total nonperforming and restructured assets	$ 43,980	$ 39,339