Employee Benefit Plans - Schedule of Assets by Investment Type (Detail)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	52.93%	48.01%	51.42%
Chesapeake Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	37.64%	39.62%	37.31%
Chesapeake Pension Plan | Other
Asset Category
Percentage of assets by investment type	9.43%	12.37%	11.27%
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	53.18%	48.56%	52.62%
FPU Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	37.74%	41.74%	37.69%
FPU Pension Plan | Other
Asset Category
Percentage of assets by investment type	9.08%	9.70%	9.69%