Employee Benefit Plans - Amounts in Accumulated Other Comprehensive Income/Loss and Regulatory Asset (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Accumulated Other Comprehensive Income Loss Tax Effect	$ 3,700,000
Prior service cost (credit)	(68,000)
Net loss	993,000
Amortization of pre-merger regulatory asset	769,000
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	364,000
Amortization of pre-merger regulatory asset	0	0	0
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	454,000
Amortization of pre-merger regulatory asset	761,000	761,000	761,000
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	9,000
Net loss	99,000
Amortization of pre-merger regulatory asset	0
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(77,000)
Net loss	70,000
Amortization of pre-merger regulatory asset	0
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	6,000
Amortization of pre-merger regulatory asset	$ 8,000	$ 8,000	$ 8,000