XML 67 R55.htm IDEA: XBRL DOCUMENT v3.8.0.1
Benefit Plans - Additional Information (Detail) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]    
Number of highest-paid consecutive years for benefits 5 years  
Defined benefit pension plan    
Defined Benefit Plan Disclosure [Line Items]    
Minimum eligibility for full-time employees, age 21 years  
Amount contributed to pension plan, expected in future   $ 2.1
Defined benefit pension plan | Minimum    
Defined Benefit Plan Disclosure [Line Items]    
Period of service credit by employee 1 year