Retirement Plans - Schedule of Projected Benefit Obligation, Accumulated Benefit Obligation and Fair Value of Plan Assets for Qualified and Non-Qualified Pension Plans (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 151,015	$ 156,924	$ 139,731
Accumulated benefit obligation	150,754	156,589
Fair value of plan assets	132,762	140,140	$ 139,737
Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	130,797	135,998
Accumulated benefit obligation	130,797	135,998
Fair value of plan assets	132,762	140,140
Non-Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	20,218	20,926
Accumulated benefit obligation	$ 19,957	$ 20,591