Retirement Plans - Defined Benefit Pension Plans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Transition obligation	$ 4	$ 7
Prior service cost	(248)	(75)
Net actuarial loss	5,596	4,782
Amount included in accumulated other comprehensive loss	5,352	4,714
Deferred tax benefit	(2,250)	(1,982)
Amount included in accumulated other comprehensive loss, net of tax	$ 3,102	$ 2,732