Annual report pursuant to Section 13 and 15(d)

Retirement Plans and Related Post Retirement Benefits - Assumptions Used to Calculate the Post Retirement Benefit Obligation (Detail)

v3.6.0.2
Retirement Plans and Related Post Retirement Benefits - Assumptions Used to Calculate the Post Retirement Benefit Obligation (Detail)
Dec. 31, 2016
Dec. 31, 2015
SERP    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Discount Rate 4.20% 4.45%
SERP Medical    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Discount Rate 4.20% 4.45%
Minimum | SERP    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Future Average Compensation Increases 3.00% 3.00%
Maximum | SERP    
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]    
Future Average Compensation Increases 5.00% 5.00%