Employee Benefit Plans - Schedule of Amounts Related to Plan recognized as Component of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan [Abstract]
Net actuarial loss	$ 6,784	$ 2,914	$ 2,402
Prior service cost	0	0	(1)
Actuarial loss	(4,553)	(4,921)	(4,980)
Total recognized in other comprehensive income	$ 2,231	$ (2,007)	$ (2,579)