Defined Benefit Pension Plan and Postretirement Benefits - Net Periodic Benefit Cost for Pension Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost	$ 405	$ 448	$ 443
Interest cost	254	196	194
Recognized actuarial (gains)	(86)	(58)	(43)
Net periodic benefit cost	573	586	594
Unrealized net actuarial (gains), net of tax	(2,324)	(2,256)	(1,574)
Total amount recognized in net periodic benefit cost and accumulated other comprehensive income (loss)	$ (1,751)	$ (1,670)	$ (980)