Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Detail) - Pension Benefits [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,403	$ 1,927	$ 4,790	$ 3,836
Interest cost	24,631	25,530	49,243	51,032
Expected return on plan assets	(37,675)	(36,234)	(75,322)	(72,431)
Amortization of prior service credit	(141)	(468)	(282)	(932)
Amortization of actuarial loss	9,628	6,613	19,241	13,208
Net periodic benefit income	$ (1,154)	$ (2,632)	$ (2,330)	$ (5,287)