Employee Benefit Plans - Schedule of Assets by Investment Type (Detail)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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	49.02%	52.70%	52.93%
Chesapeake Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	40.98%	37.79%	37.64%
Chesapeake Pension Plan | Other
Asset Category
Percentage of assets by investment type	10.00%	9.51%	9.43%
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	50.04%	55.17%	53.18%
FPU Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	41.06%	36.56%	37.74%
FPU Pension Plan | Other
Asset Category
Percentage of assets by investment type	8.90%	8.27%	9.08%