Employee Benefit Plans - Component of Net Periodic Pension Cost (Benefit) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of net periodic cost:
Interest cost		$ 74	$ 83	$ 89
Expected Amortization Of Pre Merger Regulatory Asset		0
Assumptions
Defined Benefit Plan, Plan Assets, Amount		54,333	52,250
Chesapeake Postretirement Plan
Components of net periodic cost:
Interest cost		39	38	41
Amortization of prior service cost		(77)	(77)	(77)
Actuarial (gain) loss		46	58	53
Net periodic pension cost		8	19	17
Expected Amortization Of Pre Merger Regulatory Asset			0	0
Net periodic postretirement cost		$ 8	$ 19	$ 17
Assumptions
Discount rate		4.00%	3.50%	3.75%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		$ 149	$ 136
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		73	(131)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(163)	(169)
Defined Benefit Plan, Plan Assets, Amount		0	0	$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	[1]	14	33
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		149	136
Defined Benefit Plan, Plan Assets, Benefits Paid		(163)	(169)
Funded status		(1,100)	(1,002)
Accrued pension cost		$ (1,100)	$ (1,002)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.00%	4.00%
FPU Medical Plan
Components of net periodic cost:
Interest cost		$ 48	$ 47	50
Amortization of prior service cost		0	0	0
Actuarial (gain) loss		0	0	0
Net periodic pension cost		48	47	50
Amortization of pre-merger regulatory asset		8	8	8
Net periodic postretirement cost		$ 56	$ 55	$ 58
Assumptions
Discount rate		4.25%	3.75%	4.00%
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		$ 38	$ 41
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		47	(89)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(96)	(99)
Defined Benefit Plan, Plan Assets, Amount		0	0	$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	[1]	58	58
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		38	41
Defined Benefit Plan, Plan Assets, Benefits Paid		(96)	(99)
Funded status		(1,224)	(1,187)
Accrued pension cost		$ (1,224)	$ (1,187)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.25%	4.25%
Chesapeake SERP
Components of net periodic cost:
Interest cost		$ 74	$ 83
Actuarial (gain) loss		85	101	87
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		58
Net periodic postretirement cost		$ 217	$ 184	$ 176
Assumptions
Discount rate		4.00%	3.50%	3.75%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ 159	$ (74)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(361)	(152)
Defined Benefit Plan, Plan Assets, Contributions by Employer		361	152
Defined Benefit Plan, Plan Assets, Benefits Paid		(361)	(152)
Funded status		(2,157)	(2,285)
Accrued pension cost		$ (2,157)	$ (2,285)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.00%	4.00%
Chesapeake Pension Plan
Components of net periodic cost:
Interest cost		$ 375	$ 384	$ 402
Expected return on assets		(487)	(542)	(495)
Actuarial (gain) loss		391	343	399
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		1,982	0	0
Net periodic pension cost		2,261	185	306
Amortization of pre-merger regulatory asset		0	0	0
Net periodic postretirement cost		$ 2,261	$ 185	$ 306
Assumptions
Discount rate		3.00%	3.50%	3.75%
Expected return on plan assets		6.00%	6.00%	6.00%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ 1,443	$ (610)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(483)	(505)
Defined Benefit Plan, Plan Assets, Amount		4,630	8,649	$ 9,350
Defined Benefit Plan, Plan Assets, Contributions by Employer		1,117	451
Defined Benefit Plan, Plan Assets, Benefits Paid		(483)	(505)
Funded status		(1,584)	(2,063)
Accrued pension cost		$ (1,584)	$ (2,063)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.00%	4.00%
FPU Pension Plan
Components of net periodic cost:
Interest cost		$ 2,452	$ 2,339	2,482
Expected return on assets		(2,770)	(3,091)	(2,779)
Actuarial (gain) loss		505	404	513
Net periodic pension cost		187	(348)	216
Amortization of pre-merger regulatory asset		543	761	761
Net periodic postretirement cost		$ 730	$ 413	$ 977
Assumptions
Discount rate		4.25%	3.75%	4.00%
Expected return on plan assets		6.50%	6.50%	6.50%
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ 6,508	$ (4,739)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(3,033)	(2,887)
Defined Benefit Plan, Plan Assets, Amount		49,703	43,601	$ 48,396
Defined Benefit Plan, Plan Assets, Contributions by Employer		1,157	1,205
Defined Benefit Plan, Plan Assets, Benefits Paid		(3,033)	(2,887)
Funded status		(15,601)	(15,776)
Accrued pension cost		$ (15,601)	$ (15,776)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.25%	4.25%

[1] The Chesapeake Postretirement Plan does not receive a Medicare Part-D subsidy. The FPU Medical Plan did not receive a significant subsidy for the post-merger period.