Employee Benefit Plans - Schedule of Assets by Investment Type (Detail)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Chesapeake Pension Plan [Member]
Asset Category
Percentage of assets by investment type	100.00%	100.00%	100.00%
Chesapeake Pension Plan [Member] | Investments in equity securities [Member]
Asset Category
Percentage of assets by investment type	52.07%	51.75%	64.33%
Chesapeake Pension Plan [Member] | Debt securities [Member]
Asset Category
Percentage of assets by investment type	38.00%	37.88%	30.60%
Chesapeake Pension Plan [Member] | Other [Member]
Asset Category
Percentage of assets by investment type	9.93%	10.37%	5.07%
FPU Pension Plan [Member]
Asset Category
Percentage of assets by investment type	100.00%	100.00%	100.00%
FPU Pension Plan [Member] | Investments in equity securities [Member]
Asset Category
Percentage of assets by investment type	52.81%	51.98%	60.00%
FPU Pension Plan [Member] | Debt securities [Member]
Asset Category
Percentage of assets by investment type	38.04%	38.05%	35.00%
FPU Pension Plan [Member] | Other [Member]
Asset Category
Percentage of assets by investment type	9.15%	9.97%	5.00%