Loans and Allowance for Loan Losses - Summary of Nonperforming and Restructured Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Summary Of Nonperforming And Restructured Assets [Abstract]
Past due 90 days or more and still accruing	$ 3,900	$ 2,893
Nonaccrual	31,849	31,943
Restructured	12,945	4,720
Total nonperforming and restructured loans	48,694	39,556
Other real estate owned and repossessed assets	3,676	4,424
Total nonperforming and restructured assets	$ 52,370	$ 43,980