Retirement Plans - Information Pertaining to Activity in Supplemental Retirement Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Benefit obligation at beginning of year	$ (29,196)	$ (28,472)
Service cost	(879)	(973)	$ (941)
Interest cost	(1,131)	(949)	(991)
Actuarial (loss)/gain	(6,747)	92
Plan amendments	0	0
Benefits paid	1,216	1,106
Benefit obligation at end of year	(36,737)	(29,196)	(28,472)
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Fair value of plan assets at end of year	0	0	$ 0
Funded status	(36,737)	(29,196)
Unrecognized net obligation existing at January 1, 1986	1	3
Unrecognized net actuarial loss	11,333	4,993
Unrecognized prior service cost	(141)	(194)
Accumulated other comprehensive income	(11,193)	(4,802)
Accrued benefit cost	(36,737)	(29,196)
Accumulated benefit obligation	$ (35,981)	$ (27,544)