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, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		$ (678)
Net loss		25,829
Total		25,151
Accumulated other comprehensive loss pre-tax		8,869
Post-merger regulatory asset		16,282
Subtotal		25,151
Pre-merger regulatory asset		2,095
Total unrecognized cost		27,246
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		4,223
Total		4,223
Accumulated other comprehensive loss pre-tax	[1]	4,223
Post-merger regulatory asset		0
Subtotal		4,223
Pre-merger regulatory asset		0
Total unrecognized cost		4,223
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		20,043
Total		20,043
Accumulated other comprehensive loss pre-tax	[1]	3,808
Post-merger regulatory asset		16,235
Subtotal		20,043
Pre-merger regulatory asset		2,065
Total unrecognized cost		22,108
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		757
Total		757
Accumulated other comprehensive loss pre-tax	[1]	757
Post-merger regulatory asset		0
Subtotal		757
Pre-merger regulatory asset		0
Total unrecognized cost		757
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		(678)
Net loss		748
Total		70
Accumulated other comprehensive loss pre-tax	[1]	70
Post-merger regulatory asset		0
Subtotal		70
Pre-merger regulatory asset		0
Total unrecognized cost		70
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		58
Total		58
Accumulated other comprehensive loss pre-tax	[1]	11
Post-merger regulatory asset		47
Subtotal		58
Pre-merger regulatory asset		30	$ 38
Total unrecognized cost		$ 88

[1] The total amount of accumulated other comprehensive loss recorded on our consolidated balance sheet as of December 31, 2016 is net of income tax benefits of $3.5 million.