Pension and Other Postretirement Employee Benefit Plans Components of Net Periodic Cost of Pension and Other Postretirement Employee Benefit Plans (Detail 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 398	$ 316
Interest cost	3,628	3,490
Expected return on plan assets	(4,883)	(4,984)
Amortization of prior service cost (credit)	5	18
Amortization of actuarial loss	2,884	3,083
Net periodic cost	2,032	1,923
Other Postretirement Employee Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	74	148
Interest cost	766	1,048
Expected return on plan assets	0	0
Amortization of prior service cost (credit)	(428)	(545)
Amortization of actuarial loss	(1,383)	0
Net periodic cost	$ (971)	$ 651