Employee Benefit Plans - Components of Net Periodic Defined Benefit Cost (Income) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 631	$ 609	$ 1,903	$ 1,707
Expected return on plan assets	(856)	(990)	(2,564)	(2,976)
Recognized actuarial (gain) losses	267	306	721	921
Total	42	(75)	60	(348)
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	29	26	86	78
Amortization of prior service credit	(161)	(172)	(483)	(514)
Recognized actuarial (gain) losses	(44)	(37)	(132)	(111)
Total	$ (176)	$ (183)	$ (529)	$ (547)