Benefit Plans - Benefit Obligation and Plan Asset Rollforward (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Change in benefit obligation:
Benefit obligation at beginning of year	$ 28,878	$ 31,970	$ 29,533
Service cost	0	0	0
Interest cost	1,198	1,094	1,227
Actuarial loss	63	0	0
Benefits paid	(1,493)	(1,401)	(1,590)
Change in actuarial assumptions	4,412	(2,785)	2,800
Benefit obligation at end of year	33,058	28,878	31,970
Change in plan assets:
Fair value of plan assets at beginning of year	43,449	46,870	43,153
Actual return on plan assets	7,976	(2,020)	5,307
Employer contributions	0	0	0
Benefits paid	(1,493)	(1,401)	(1,590)
Fair value of plan assets at end of year	49,932	43,449	46,870
Funded status at end of year	16,874	14,571	14,900
Post-retirement
Change in benefit obligation:
Benefit obligation at beginning of year	20,028	22,757	20,805
Service cost	80	115	105
Interest cost	837	786	871
Actuarial loss	0	18	0
Benefits paid	(600)	(590)	(560)
Change in actuarial assumptions	2,978	(3,058)	1,536
Benefit obligation at end of year	23,323	20,028	22,757
Change in plan assets:
Fair value of plan assets at beginning of year	0	0	0
Actual return on plan assets	0	0	0
Employer contributions	600	590	560
Benefits paid	(600)	(590)	(560)
Fair value of plan assets at end of year	0	0	0
Funded status at end of year	$ (23,323)	$ (20,028)	$ (22,757)