Pension Plans - 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	$ 22	$ 65	$ 188	$ 192
Interest cost	346	363	1,012	1,092
Expected return on plan assets	(612)	(476)	(1,603)	(1,427)
Recognized net actuarial loss	151	80	393	324
Net periodic pension cost (benefit)	$ (93)	$ 32	$ (10)	$ 181