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, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		$ (601)
Net loss		22,622
Total		22,021
Accumulated other comprehensive loss pre-tax		7,852
Post-merger regulatory asset		14,169
Subtotal		22,021
Pre-merger regulatory asset		1,326
Total unrecognized cost		23,347
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		3,629
Total		3,629
Accumulated other comprehensive loss pre-tax	[1]	3,629
Post-merger regulatory asset		0
Subtotal		3,629
Pre-merger regulatory asset		0
Total unrecognized cost		3,629
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		17,483
Total		17,483
Accumulated other comprehensive loss pre-tax	[1]	3,322
Post-merger regulatory asset		14,161
Subtotal		17,483
Pre-merger regulatory asset		1,304
Total unrecognized cost		18,787
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		733
Total		733
Accumulated other comprehensive loss pre-tax	[1]	733
Post-merger regulatory asset		0
Subtotal		733
Pre-merger regulatory asset		0
Total unrecognized cost		733
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		(601)
Net loss		767
Total		166
Accumulated other comprehensive loss pre-tax	[1]	166
Post-merger regulatory asset		0
Subtotal		166
Pre-merger regulatory asset		0
Total unrecognized cost		166
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)		0
Net loss		10
Total		10
Accumulated other comprehensive loss pre-tax	[1]	2
Post-merger regulatory asset		8
Subtotal		10
Pre-merger regulatory asset		22	$ 30
Total unrecognized cost		$ 32

[1] The total amount of accumulated other comprehensive loss recorded on our consolidated balance sheet as of December 31, 2017 is net of income tax benefits of $3.1 million.