Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Detail) - Pension Benefits [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,240	$ 2,106	$ 6,530	$ 6,257
Interest cost	24,243	26,195	72,474	78,505
Expected return on plan assets	(38,061)	(39,296)	(117,475)	(117,767)
Amortization of prior service credit	(88)	(108)	(263)	(324)
Amortization of actuarial loss	9,549	7,860	28,500	23,530
Net periodic benefit income	$ (2,117)	$ (3,243)	$ (10,234)	$ (9,799)