Retirement Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Employee hire date no longer eligible for noncontributory retirement plan	Dec. 08, 2009
Defined benefit plan, expected long-term rate of return	7.00%
Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	60.00%
Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, target allocation, percentage	40.00%
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation arrangement with individual, compensation expense	$ 134	$ 215	$ 222
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions for next fiscal year	$ 159
Defined benefit plan, expected long-term rate of return	7.00%	7.00%
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions for next fiscal year	$ 89
Defined benefit plan, expected long-term rate of return	0.00%	0.00%
Deferred Salary Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	$ 1,500	$ 1,400	$ 1,400