Annual report pursuant to Section 13 and 15(d)

Employee Benefits - Additional Information (Detail)

v3.8.0.1
Employee Benefits - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Bank-Owned Life Insurance [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Cash surrender value $ 50.6    
Section 401(k) Plan [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Percent of participant contributions (percent) 75.00%    
Percent of employer contribution (up to, percent) 8.00%    
Contributions $ 2.0 $ 1.9 $ 1.6