Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Components of net periodic cost:
Interest cost	$ 63	$ 74		$ 83
Expected Amortization Of Pre Merger Regulatory Asset	0
Chesapeake Postretirement Plan
Components of net periodic cost:
Interest cost	26	39		38
Amortization of prior service cost	(77)	(77)		(77)
Actuarial (gain) loss	24	46		58
Net periodic pension cost	(27)	8		19
Expected Amortization Of Pre Merger Regulatory Asset		0		0
Net periodic postretirement cost	$ (27)	$ 8		$ 19
Assumptions
Discount rate	3.00%	4.00%		3.50%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	$ 166	$ 149
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(34)	73
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(225)	(163)
Defined Benefit Plan, Plan Assets, Amount	0	0		$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	59	14
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	166	149
Defined Benefit Plan, Plan Assets, Benefits Paid	(225)	(163)
Funded status	(1,033)	(1,100)
Accrued pension cost	$ (1,033)	$ (1,100)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.25%	3.00%
FPU Medical Plan
Components of net periodic cost:
Interest cost	$ 30	$ 48		47
Amortization of prior service cost	0	0		0
Actuarial (gain) loss	19	0		0
Net periodic pension cost	11	48		47
Amortization of pre-merger regulatory asset	6	8		8
Net periodic postretirement cost	$ 17	$ 56		$ 55
Assumptions
Discount rate	3.25%	4.25%		3.75%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	$ 37	$ 38
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(181)	47
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(101)	(96)
Defined Benefit Plan, Plan Assets, Amount	0	0		$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	64	58
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	37	38
Defined Benefit Plan, Plan Assets, Benefits Paid	(101)	(96)
Funded status	(1,009)	(1,224)
Accrued pension cost	$ (1,009)	$ (1,224)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.50%	3.25%
Chesapeake SERP
Components of net periodic cost:
Interest cost	$ 63	$ 74
Actuarial (gain) loss	20	85		101
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	58
Net periodic postretirement cost	$ 83	$ 217		$ 184
Assumptions
Discount rate	3.00%	4.00%		3.50%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ 144	$ 159
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(152)	(361)
Defined Benefit Plan, Plan Assets, Contributions by Employer	152	361
Defined Benefit Plan, Plan Assets, Benefits Paid	(152)	(361)
Funded status	(2,212)	(2,157)
Accrued pension cost	$ (2,212)	$ (2,157)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.25%	3.00%
Chesapeake Pension Plan
Components of net periodic cost:
Interest cost	$ 176	$ 375	[1]	$ 384
Expected return on assets	(157)	(487)	[1]	(542)
Actuarial (gain) loss	243	391	[1]	343
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	203	1,982	[1]	0
Net periodic pension cost	465	2,261	[1]	185
Amortization of pre-merger regulatory asset	0	0	[1]	0
Net periodic postretirement cost	$ 465	$ 2,261	[1]	$ 185
Assumptions
Discount rate	3.00%	3.00%		3.50%
Expected return on plan assets	3.50%	6.00%		6.00%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ 450	$ 1,443
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(82)	(483)
Defined Benefit Plan, Plan Assets, Amount	4,609	4,630		$ 8,649
Defined Benefit Plan, Plan Assets, Contributions by Employer	304	1,117
Defined Benefit Plan, Plan Assets, Benefits Paid	(82)	(483)
Funded status	(1,537)	(1,584)
Accrued pension cost	$ (1,537)	$ (1,584)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.25%	3.00%
FPU Pension Plan
Components of net periodic cost:
Interest cost	$ 2,085	$ 2,452		2,339
Expected return on assets	(2,967)	(2,770)		(3,091)
Actuarial (gain) loss	552	505		404
Net periodic pension cost	(330)	187		(348)
Amortization of pre-merger regulatory asset	0	543		761
Net periodic postretirement cost	$ (330)	$ 730		$ 413
Assumptions
Discount rate	3.25%	4.25%		3.75%
Expected return on plan assets	6.00%	6.50%		6.50%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ 6,069	$ 6,508
Defined Benefit Plan, Benefit Obligation, Benefits Paid	(3,092)	(3,033)
Defined Benefit Plan, Plan Assets, Amount	55,966	49,703		$ 43,601
Defined Benefit Plan, Plan Assets, Contributions by Employer	2,774	1,157
Defined Benefit Plan, Plan Assets, Benefits Paid	(3,092)	(3,033)
Funded status	(14,400)	(15,601)
Accrued pension cost	$ (14,400)	$ (15,601)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.50%	3.25%

[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.