Annual report pursuant to Section 13 and 15(d)

Retirement Plans and Related Post Retirement Benefits - Assumptions Used to Determine the Net Periodic Cost (Detail)

v3.7.0.1
Retirement Plans and Related Post Retirement Benefits - Assumptions Used to Determine the Net Periodic Cost (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
SERP      
Defined Benefit Plan Disclosure      
Discount Rate 4.45% 4.05% 5.10%
Future Average Compensation Increases   5.00% 5.00%
SERP | Minimum      
Defined Benefit Plan Disclosure      
Future Average Compensation Increases 3.00%    
SERP | Maximum      
Defined Benefit Plan Disclosure      
Future Average Compensation Increases 5.00%    
SERP Medical      
Defined Benefit Plan Disclosure      
Discount Rate 4.45% 4.05% 5.10%
Future Average Compensation Increases 5.72% 5.32% 5.48%