Employee Benefit Plans - Amounts Included in Regulatory Asset and Accumulated Other Comprehensive Income/Loss Recognized as Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	$ (14)
Net loss	172
Total recognized in net periodic benefit cost	158
Recognized from accumulated other comprehensive loss	92
Recognized from regulatory asset	66
Total	158
Chesapeake Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)		(1)
Net loss	57	85
Total recognized in net periodic benefit cost	57
Recognized from accumulated other comprehensive loss	57
Total	57
FPU Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	81	44
Total recognized in net periodic benefit cost	81
Recognized from accumulated other comprehensive loss	15
Recognized from regulatory asset	66
Total	81
Chesapeake Pension SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	5	5
Net loss	16	11
Total recognized in net periodic benefit cost	21
Recognized from accumulated other comprehensive loss	21
Total	21
Chesapeake Postretirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	(19)	(20)
Net loss	18	18
Total recognized in net periodic benefit cost	(1)
Recognized from accumulated other comprehensive loss	(1)
Total	$ (1)