Pension Benefit and Retirement Health and Life Insurance Benefits (Additional Information) (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2014 USD ($)	Jun. 30, 2013 USD ($)	Dec. 31, 2015 USD ($) plan	Dec. 31, 2014 USD ($)	Dec. 31, 2013 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	$ 155,200		$ 151,900	$ 155,200
Accumulated benefit obligation of plan with accumulated benefit obligation in excess of plan assets	155,200		151,900	155,200
Fair value of the plan assets of plan with accumulated benefit obligation in excess of plan assets	137,600		139,300	137,600
Projected benefit obligation of plan with plan assets in excess of accumulated benefit obligation	32,600		30,500	32,600
Accumulated benefit obligation of plan with plan assets in excess of accumulated benefit obligation	32,600		30,500	32,600
Fair value of the plan assets of plan with plan assets in excess of accumulated benefit obligation	33,000		$ 31,700	$ 33,000
Change in discount rate			0.25%
Discount rate			4.25%	4.00%
Health care cost trend rate annual change			0.50%
Percentage point change in assumed health care cost trend rates			1.00%
Health care cost, employees age			65 years
Estimated employer contributions in 2015			$ 300
Employer contributions			$ 6,500	$ 13,000
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%	7.50%
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]
Defined benefit plan, one-time cash payment			$ 8,541	$ 24,934
Settlement charge	$ 5,200		0	3,530
Curtailment charges		$ 1,500	0	$ 0	$ (1,537)
Net loss to be recognized over next twelve months			$ 1,800
Discount rate			4.00%	4.75%
Historical return on plan assets over 20 years			8.40%
Hypothetical long-term return on assets over last 20 years			8.50%
Hypothetical long-term return on assets over the last 10 years			7.50%
Expected long-term rate of return on plan assets			6.50%
Employer contributions			$ 6,971	$ 13,871
Pension Benefits | Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan asset allocations	23.00%		27.00%	23.00%
Pension Benefits | Debt Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan asset allocations	77.00%		73.00%	77.00%
Retirement Health and Life Insurance Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, one-time cash payment			$ 766	$ 775
Settlement charge			0	0
Curtailment charges			0	$ 0	$ 0
Net loss to be recognized over next twelve months			$ 1,600
Discount rate			3.00%	3.25%
Employer contributions			$ 766	$ 775
Bear Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Remaining required employer contributions			$ 300