Employee Benefit Plans - Components of Net Periodic Defined Benefit Cost (Income) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 372	$ 506	$ 1,116	$ 1,518
Expected return on plan assets	(590)	(689)	(1,770)	(2,067)
Recognized actuarial (gains) losses	365	394	1,095	1,182
Total	147	211	441	633
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	15	20	45	60
Recognized actuarial (gains) losses	(63)	(54)	(189)	(162)
Total	$ (48)	$ (34)	$ (144)	$ (102)