Pension Benefit Plan - Summarization of Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 294	$ 327	$ 905	$ 930
Interest cost	179	158	551	448
Expected return on plan assets	(381)	(329)	(1,174)	(935)
Amortization of actuarial losses	61	80	188	228
Net periodic pension cost	$ 153	$ 236	$ 470	$ 671