Employee Benefit Plans - Schedule of Assets by Investment Type (Detail)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	48.01%	51.42%	54.40%
Chesapeake Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	39.62%	37.31%	36.54%
Chesapeake Pension Plan | Other
Asset Category
Percentage of assets by investment type	12.37%	11.27%	9.06%
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	48.56%	52.62%	55.02%
FPU Pension Plan | Debt securities
Asset Category
Percentage of assets by investment type	41.74%	37.69%	36.54%
FPU Pension Plan | Other
Asset Category
Percentage of assets by investment type	9.70%	9.69%	8.44%