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		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		$ (755)
Net loss		26,602
Total		25,847
Accumulated other comprehensive loss pre-tax	[1]	9,235
Post-merger regulatory asset		16,612
Subtotal		25,847
Pre-merger regulatory asset		2,864
Total unrecognized cost		28,711
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		4,434
Total		4,434
Accumulated other comprehensive loss pre-tax	[1]	4,434
Post-merger regulatory asset		0
Subtotal		4,434
Pre-merger regulatory asset		0
Total unrecognized cost		4,434
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		20,410
Total		20,410
Accumulated other comprehensive loss pre-tax	[1]	3,878
Post-merger regulatory asset		16,532
Subtotal		20,410
Pre-merger regulatory asset		2,826
Total unrecognized cost		23,236
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		866
Total		866
Accumulated other comprehensive loss pre-tax	[1]	866
Post-merger regulatory asset		0
Subtotal		866
Pre-merger regulatory asset		0
Total unrecognized cost		866
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		(755)
Net loss		793
Total		38
Accumulated other comprehensive loss pre-tax	[1]	38
Post-merger regulatory asset		0
Subtotal		38
Pre-merger regulatory asset		0
Total unrecognized cost		38
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		99
Total		99
Accumulated other comprehensive loss pre-tax	[1]	19
Post-merger regulatory asset		80
Subtotal		99
Pre-merger regulatory asset		38	$ 46
Total unrecognized cost		$ 137

[1] The total amount of accumulated other comprehensive loss recorded on our consolidated balance sheet as of December 31, 2015 is net of income tax benefits of $3.7 million.