Retirement Plans - Components of Net Periodic Benefit Cost (Detail) - United States - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ (28)	$ 26	$ 10	$ 53
Interest cost	418	474	1,256	1,422
Recognized net actuarial loss	522	456	1,566	1,367
Net periodic benefit cost	$ 912	$ 956	$ 2,832	$ 2,842