Employee Benefit Plans - Components of Net Periodic Defined Benefit Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2,302	$ 2,376	$ 2,538
Expected return on plan assets	(2,911)	(3,353)	(3,409)
Amortization of actuarial (gain) loss	1,474	1,340	934
Total	865	363	63
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	96	108	114
Amortization of actuarial (gain) loss	(152)	(101)	(176)
Amortization of prior service credit	(541)	(621)	(644)
Total	$ (597)	$ (614)	$ (706)