Employee Benefit Plans - Amounts in Accumulated Other Comprehensive Income/Loss and Regulatory Asset (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)	$ (59)
Net loss	778
Amortization of pre-merger regulatory asset	769
Chesapeake Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(1)
Net loss	308
FPU Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss	332
Amortization of pre-merger regulatory asset	761	761	888
Chesapeake SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	19
Net loss	64
Chesapeake Postretirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(77)
Net loss	74
Amortization of pre-merger regulatory asset
FPU Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)
Net loss
Amortization of pre-merger regulatory asset	$ 8