Retirement Plans and Other Postretirement Benefits - Summary of Retirement Plans and Other Postretirement Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Fair value of plan assets at beginning of year	$ 45,379
Fair value of plan assets at end of year	51,607	$ 45,379
Retirement Plans [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	46,868	50,364
Service cost	436	560	$ 524
Interest cost	1,905	1,760	1,927
Actuarial loss (gain)	7,104	(3,205)
Benefits paid	(2,628)	(2,611)
Benefit obligation at end of year	53,685	46,868	50,364
Change in plan assets:
Fair value of plan assets at beginning of year	45,379	46,753
Actual return (loss) on plan assets	8,696	(1,923)
Benefits paid	(2,628)	(2,611)
Employer contribution and non-qualified benefit payments	160	3,160
Fair value of plan assets at end of year	51,607	45,379	46,753
Funded status	(2,078)	(1,489)
Unrecognized net actuarial loss (gain)	22,433	22,141
Unrecognized prior service costs	0	(181)
Net amount recognized	20,355	20,471
Other Post Retirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	2,283	2,611
Service cost	67	88	48
Interest cost	94	92	118
Actuarial loss (gain)	731	(404)
Benefits paid	(106)	(104)
Benefit obligation at end of year	3,069	2,283	2,611
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Actual return (loss) on plan assets	0	0
Benefits paid	(106)	(104)
Employer contribution and non-qualified benefit payments	106	104
Fair value of plan assets at end of year	0	0	$ 0
Funded status	(3,069)	(2,283)
Unrecognized net actuarial loss (gain)	638	(92)
Unrecognized prior service costs	0	0
Net amount recognized	$ (2,431)	$ (2,375)