Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Detail) - Pension Benefits [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,157	$ 2,027
Interest cost	24,132	26,091
Expected return on plan assets	(39,733)	(39,138)
Amortization of prior service credit	(88)	(108)
Amortization of actuarial loss	9,485	7,795
Net periodic benefit income	$ (4,047)	$ (3,333)