Pension Plans and Defined Contribution Plan - Schedule of Pension Plan Investment Allocations (Detail) - Pension Plans [Member]	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	100.00%	100.00%
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	0.60%	0.40%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	50.80%	37.80%
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	27.40%	40.50%
Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	4.80%	10.80%
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	11.90%	10.50%
Master Limited Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	4.50%