Employee Benefit Plans - Schedule of Amounts Not Yet Reflected in Net Periodic Benefit Cost and Included in Accumulated Other Comprehensive Income Loss or Regulatory Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	$ (823)
Net loss	26,296
Total	25,473
Accumulated other comprehensive loss pre-tax	9,344
Post-merger regulatory asset	16,129
Subtotal	25,473
Pre-merger regulatory asset	3,633
Total unrecognized cost	29,106
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	4,410
Total	4,410
Accumulated other comprehensive loss pre-tax	4,410
Post-merger regulatory asset	0
Subtotal	4,410
Pre-merger regulatory asset	0
Total unrecognized cost	4,410
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	19,679
Total	19,679
Accumulated other comprehensive loss pre-tax	3,739
Post-merger regulatory asset	15,940
Subtotal	19,679
Pre-merger regulatory asset	3,587	4,300
Total unrecognized cost	23,266
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	9
Net loss	1,050
Total	1,059
Accumulated other comprehensive loss pre-tax	1,059
Post-merger regulatory asset	0
Subtotal	1,059
Pre-merger regulatory asset	0
Total unrecognized cost	1,059
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(832)
Net loss	924
Total	92
Accumulated other comprehensive loss pre-tax	92
Post-merger regulatory asset	0
Subtotal	92
Pre-merger regulatory asset	0
Total unrecognized cost	92
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	0
Net loss	233
Total	233
Accumulated other comprehensive loss pre-tax	44
Post-merger regulatory asset	189
Subtotal	233
Pre-merger regulatory asset	46	54
Total unrecognized cost	$ 279