Employee Benefit Plans - Components of Net Periodic Defined Benefit Cost (Income) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 597	$ 631	$ 1,801	$ 1,903
Expected return on plan assets	(840)	(856)	(2,516)	(2,564)
Recognized actuarial (gain) losses	349	267	1,025	721
Total	106	42	310	60
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	27	29	81	86
Amortization of prior service credit	(155)	(161)	(466)	(483)
Recognized actuarial (gain) losses	(25)	(44)	(76)	(132)
Total	$ (153)	$ (176)	$ (461)	$ (529)