Benefit Plans - Defined Benefit Pension Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Net Periodic Benefit Cost [Abstract]
Service cost – benefits earned during year	$ 567	$ 715	$ 1,681	$ 2,121
Interest cost on projected benefit obligation	1,327	1,242	3,938	3,684
Expected return on plan assets	(2,235)	(2,416)	(6,633)	(7,169)
Amortization of prior service cost	7	6	20	19
Amortization of net loss	817	766	2,424	2,274
Net periodic pension cost	$ 483	$ 313	$ 1,430	$ 929