Employee Benefit Plans - Amounts in Accumulated Other Comprehensive Income/Loss and Regulatory Asset (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Accumulated Other Comprehensive Income Loss Tax Effect	$ 3,700
Prior service cost (credit)	(77)
Net loss	1,078
Amortization of pre-merger regulatory asset	769
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	412
Amortization of pre-merger regulatory asset	0	$ 0	$ 0
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amortization of Transition Obligations (Assets)	2,800	3,600
Prior service cost (credit)	0
Net loss	512
Amortization of pre-merger regulatory asset	761	761	761
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	87
Amortization of pre-merger regulatory asset	0
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(77)
Net loss	67
Amortization of pre-merger regulatory asset	0
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	0
Amortization of pre-merger regulatory asset	$ 8	$ 8	$ 8