Employee Benefit Plans (Disaggregated Information Related to Corporations Defined Benefit Pension Plans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 194,140	$ 199,637	$ 163,876	$ 178,158
Accumulated benefit obligation	194,140	199,637	163,876
Fair value of plan assets	163,270	168,185	164,769	$ 145,901
Funded status of the plan at end of year and accrued (benefit) liability recognized	30,870	31,452	$ (893)
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	174,429	179,970
Accumulated benefit obligation	174,429	179,970
Fair value of plan assets	163,270	168,185
Funded status of the plan at end of year and accrued (benefit) liability recognized	11,159	11,785
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	19,711	19,667
Accumulated benefit obligation	19,711	19,667
Fair value of plan assets	0	0
Funded status of the plan at end of year and accrued (benefit) liability recognized	$ 19,711	$ 19,667