Defined Benefit Pension Plan and Postretirement Benefits - Net Periodic Benefit Cost for Pension Plans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 105	$ 98
Interest cost	51	62
Recognized actuarial (gains)	(23)	(21)
Net periodic benefit cost	$ 133	$ 139