Retirement Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	$ 215	$ 222	$ 52
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumed discount rate	3.60%	4.00%
Settlements			(3,200)
Settlement cost	$ 0	$ 0	1,434
Expected employer contributions for next fiscal year	$ 157
Defined Benefit Plan, Expected Long-Term Rate of Return	7.00%	7.50%
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumed discount rate	3.60%	4.00%
Settlement cost	$ 0	$ 0	0
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	$ 1,400	$ 1,400	$ 1,200