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, 2014		Mar. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	$ (14)
Net loss	66
Recognized from accumulated other comprehensive loss	52	[1]
Recognized from regulatory asset	0
Total recognized in net periodic benefit cost	52
Chesapeake Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	0		0
Net loss	37		57
Recognized from accumulated other comprehensive loss	37	[1]
Total recognized in net periodic benefit cost	37
FPU Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	0		81
Recognized from accumulated other comprehensive loss	0	[1]
Recognized from regulatory asset	0
Total recognized in net periodic benefit cost	0
Chesapeake Pension SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	5		5
Net loss	12		16
Recognized from accumulated other comprehensive loss	17	[1]
Total recognized in net periodic benefit cost	17
Chesapeake Postretirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	(19)		(19)
Net loss	17		18
Recognized from accumulated other comprehensive loss	(2)	[1]
Total recognized in net periodic benefit cost	$ (2)

[1] See Note 8, Accumulated Other Comprehensive Income (Loss).