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, 2020	Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 63	$ 74		$ 83
Prior service cost (credit)		(370)
Net loss		24,326
Total		23,956
Accumulated other comprehensive loss pre-tax		6,907
Post-merger regulatory asset		(17,049)
Total unrecognized cost		(23,956)
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost		176	375	[1]	384
Prior service cost (credit)		0
Net loss		2,033
Total		2,033
Accumulated other comprehensive loss pre-tax	[2]	2,033
Post-merger regulatory asset		0
Total unrecognized cost		(2,033)
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		157	487	[1]	542
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		(243)	(391)	[1]	(343)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(203)	(1,982)	[1]	0
Net Periodic Cost Benefit		465	2,261	[1]	185
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		465	2,261	[1]	185
Amortization Of Pre Merger Regulatory Asset		$ 0	$ 0	[1]	$ 0
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.00%	3.00%		3.50%
Expected return on plan assets		3.50%	6.00%		6.00%
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 2,085	$ 2,452		$ 2,339
Prior service cost (credit)		0
Net loss		21,242
Total		21,242
Accumulated other comprehensive loss pre-tax	[2]	4,036
Post-merger regulatory asset		(17,206)
Total unrecognized cost		(21,242)
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		2,967	2,770		3,091
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		(552)	(505)		(404)
Net Periodic Cost Benefit		(330)	187		(348)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		(330)	730		413
Amortization Of Pre Merger Regulatory Asset		$ 0	$ 543		$ 761
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.25%	4.25%		3.75%
Expected return on plan assets		6.00%	6.50%		6.50%
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 63	$ 74
Prior service cost (credit)		0
Net loss		699
Total		699
Accumulated other comprehensive loss pre-tax	[2]	699
Post-merger regulatory asset		0
Total unrecognized cost		(699)
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		(20)	(85)		$ (101)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		0	(58)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		$ 83	$ 217		$ 184
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.00%	4.00%		3.50%
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 26	$ 39		$ 38
Prior service cost (credit)		(370)
Net loss		546
Total		176
Accumulated other comprehensive loss pre-tax	[2]	176
Post-merger regulatory asset		0
Total unrecognized cost		(176)
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		(24)	(46)		(58)
Net Periodic Cost Benefit		(27)	8		19
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		$ (27)	$ 8		$ 19
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.00%	4.00%		3.50%
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 30	$ 48		$ 47
Prior service cost (credit)		0
Net loss		(194)
Total		(194)
Accumulated other comprehensive loss pre-tax	[2]	(37)
Post-merger regulatory asset		(157)
Total unrecognized cost		(194)
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		(19)	0		0
Net Periodic Cost Benefit		11	48		47
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		17	56		55
Amortization Of Pre Merger Regulatory Asset		$ 6	$ 8		$ 8
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.25%	4.25%		3.75%

[1] (1) As a result of annuity purchases and lump sum payments associated with the de-risking of the Chesapeake Pension Plan, the discount rate for Chesapeake Pension Plan was remeasured which triggered settlement accounting expense in the fourth quarter of 2019. We recorded $0.7 million of the settlement expense in our consolidated statement of income which reflected a portion of the pension settlement expense that was deemed not recoverable through the regulatory process.

[2] The total amount of accumulated other comprehensive loss recorded on our consolidated balance sheet as of December 31, 2020 is net of income tax benefits of $1.8 million.