Pension Benefit and Retirement Health and Life Insurance Benefits (Additional Information) (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) plan	Dec. 31, 2015 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of defined benefit pension plans | plan		3
Projected benefit obligation of plan with accumulated benefit obligation in excess of plan assets		$ 148,600	$ 151,900
Accumulated benefit obligation of plan with accumulated benefit obligation in excess of plan assets		148,600	151,900
Fair value of the plan assets of plan with accumulated benefit obligation in excess of plan assets		140,100	139,300
Projected benefit obligation of plan with plan assets in excess of accumulated benefit obligation		29,100	30,500
Accumulated benefit obligation of plan with plan assets in excess of accumulated benefit obligation		29,100	30,500
Fair value of the plan assets of plan with plan assets in excess of accumulated benefit obligation		$ 31,700	$ 31,700
Change in discount rate			4.00%
Health care cost trend rate annual change		(0.25%)
Percentage point change in assumed health care cost trend rates		1.00%
Health care cost, employees age		65 years
Remaining required employer contributions			$ 300
Estimated employer contributions in 2017		$ 300
Employer contributions			$ 6,500
Retirees of 65 Years Old or Younger
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate assumed for next fiscal year		7.50%	7.00%
Ultimate health care cost trend rate		4.50%
Retirees of 65 Years Old or Older
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Health care cost trend rate assumed for next fiscal year		7.50%	7.50%
Ultimate health care cost trend rate		4.50%
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement charge	$ 5,200
Net loss to be recognized over next twelve months		$ 1,700
Historical return on plan assets over 20 years		8.30%
Expected long-term rate of return on plan assets		5.51%
Employer contributions		$ 344	$ 6,971
Pension Benefits | Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan asset allocations		27.00%	27.00%
Pension Benefits | Debt Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan asset allocations		73.00%	73.00%
Retirement Health and Life Insurance Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net loss to be recognized over next twelve months		$ 1,500
Employer contributions		860	$ 766
Bear Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Remaining required employer contributions		$ 300