Pension Plans and Defined Contribution Plan - Schedule of Pension Plan Investment Allocations (Detail) (Pension Plans [Member])	Dec. 31, 2014	Dec. 31, 2013
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	1.10%	1.20%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	29.60%	29.20%
Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	45.40%	42.50%
Real Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	13.60%	16.60%
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	10.30%	10.50%