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			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	$ (15)			$ (30)
Net loss	173			344
Recognized from accumulated other comprehensive loss	92	[1]		183	[1]
Recognized from regulatory asset	66			131
Total recognized in net periodic benefit cost	158			314
Chesapeake Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	0		(2)	(1)		(3)
Net loss	57		85	114		170
Recognized from accumulated other comprehensive loss	57	[1]		113	[1]
Total recognized in net periodic benefit cost	57			113
FPU Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net loss	81		44	162		88
Recognized from accumulated other comprehensive loss	15	[1]		31	[1]
Recognized from regulatory asset	66			131
Total recognized in net periodic benefit cost	81			162
Chesapeake Pension SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	5		5	10		10
Net loss	16		12	32		23
Recognized from accumulated other comprehensive loss	21	[1]		42	[1]
Total recognized in net periodic benefit cost	21			42
Chesapeake Postretirement Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Prior service cost (credit)	(20)		(20)	(39)		(40)
Net loss	19		17	36		35
Recognized from accumulated other comprehensive loss	(1)	[1]		(3)	[1]
Total recognized in net periodic benefit cost	$ (1)			$ (3)

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