Employee Benefit Plans - Schedule of Assets by Investment Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Inputs, Level 1, 2 and 3
Asset Category
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value Investments	$ 52,459	$ 47,316
Chesapeake Pension Plan
Asset Category
Percentage of assets by investment type	100.00%	100.00%	100.00%
Chesapeake Pension Plan | Investments in equity securities
Asset Category
Percentage of assets by investment type	0.00%	0.00%	49.00%
Chesapeake Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	96.00%	92.00%	41.00%
Chesapeake Pension Plan | Other
Asset Category
Percentage of assets by investment type	4.00%	8.00%	10.00%
FPU Pension Plan
Asset Category
Percentage of assets by investment type	100.00%	100.00%	100.00%
FPU Pension Plan | Investments in equity securities
Asset Category
Percentage of assets by investment type	54.00%	53.00%	50.00%
FPU Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	37.00%	37.00%	41.00%
FPU Pension Plan | Other
Asset Category
Percentage of assets by investment type	9.00%	10.00%	9.00%