Employee Benefit Plans - Schedule of Amounts Not Yet Reflected in Net Periodic Benefit Cost and Included in Accumulated Other Comprehensive Income Loss or Regulatory Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	$ (941)
Net loss	21,916
Total	20,975
Accumulated other comprehesive loss pre-tax	8,391
Post-merger regulatory asset	12,584
Subtotal	20,975
Pre-merger regulatory asset	5,171
Total unrecognized cost	26,146	23,100	13,900
Chesapeake Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(1)
Net loss	4,379
Total	4,378
Accumulated other comprehesive loss pre-tax	4,378
Subtotal	4,378
Total unrecognized cost	4,378
FPU Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss	15,517
Total	15,517
Accumulated other comprehesive loss pre-tax	2,948
Post-merger regulatory asset	12,569
Subtotal	15,517
Pre-merger regulatory asset	5,109
Total unrecognized cost	20,626
Chesapeake SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	46
Net loss	858
Total	904
Accumulated other comprehesive loss pre-tax	904
Subtotal	904
Total unrecognized cost	904
Chesapeake Postretirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(986)
Net loss	1,144
Total	158
Accumulated other comprehesive loss pre-tax	158
Subtotal	158
Total unrecognized cost	158
FPU Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)
Net loss	18
Total	18
Accumulated other comprehesive loss pre-tax	3
Post-merger regulatory asset	15
Subtotal	18
Pre-merger regulatory asset	62
Total unrecognized cost	$ 80