Employee Benefit Plans - Schedule of Funded Status of Benefit Obligation and Plan Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Change in benefit obligation:
Interest cost	$ 63	$ 74		$ 83
Chesapeake Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year	6,214	10,712
Interest cost	176	375	[1]	384
Actuarial loss	450	1,443
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	(612)	(5,833)
Benefits paid	(82)	(483)
Benefit obligation - end of year	6,146	6,214		10,712
Change in plan assets:
Balance, beginning of year	4,630	8,649
Actual return on plan assets	369	1,180
Employer contributions	304	1,117
Defined Benefit Plan, Plan Assets, Payment for Settlement	(612)	(5,833)
Benefits paid	(82)	(483)
Balance, end of year	4,609	4,630		$ 8,649
Reconciliation:
Funded status	(1,537)	(1,584)
Accrued pension cost	$ (1,537)	$ (1,584)
Assumptions:
Discount rate	2.25%	3.00%
Expected return on plan assets	3.50%	6.00%		6.00%
FPU Pension Plan
Change in benefit obligation:
Benefit obligation - beginning of year	$ 65,304	$ 59,377
Interest cost	2,085	2,452		$ 2,339
Actuarial loss	6,069	6,508
Benefits paid	(3,092)	(3,033)
Benefit obligation - end of year	70,366	65,304		59,377
Change in plan assets:
Balance, beginning of year	49,703	43,601
Actual return on plan assets	6,581	7,978
Employer contributions	2,774	1,157
Benefits paid	(3,092)	(3,033)
Balance, end of year	55,966	49,703		$ 43,601
Reconciliation:
Funded status	(14,400)	(15,601)
Accrued pension cost	$ (14,400)	$ (15,601)
Assumptions:
Discount rate	2.50%	3.25%
Expected return on plan assets	6.00%	6.50%		6.50%
Chesapeake SERP
Change in benefit obligation:
Benefit obligation - beginning of year	$ 2,157	$ 2,285
Interest cost	63	74
Actuarial loss	144	159
Benefits paid	(152)	(361)
Benefit obligation - end of year	2,212	2,157		$ 2,285
Change in plan assets:
Employer contributions	152	361
Benefits paid	(152)	(361)
Reconciliation:
Funded status	(2,212)	(2,157)
Accrued pension cost	$ (2,212)	$ (2,157)
Assumptions:
Discount rate	2.25%	3.00%
Chesapeake Postretirement Plan
Change in benefit obligation:
Benefit obligation - beginning of year	$ 1,100	$ 1,002
Interest cost	26	39		38
Plan participants contributions	166	149
Actuarial loss	(34)	73
Benefits paid	(225)	(163)
Benefit obligation - end of year	1,033	1,100		1,002
Change in plan assets:
Balance, beginning of year	0	0
Employer contributions	59	14
Plan participants contributions	166	149
Benefits paid	(225)	(163)
Balance, end of year	0	0		0
Reconciliation:
Funded status	(1,033)	(1,100)
Accrued pension cost	$ (1,033)	$ (1,100)
Assumptions:
Discount rate	2.25%	3.00%
FPU Medical Plan
Change in benefit obligation:
Benefit obligation - beginning of year	$ 1,224	$ 1,187
Interest cost	30	48		47
Plan participants contributions	37	38
Actuarial loss	(181)	47
Benefits paid	(101)	(96)
Benefit obligation - end of year	1,009	1,224		1,187
Change in plan assets:
Balance, beginning of year	0	0
Employer contributions	64	58
Plan participants contributions	37	38
Benefits paid	(101)	(96)
Balance, end of year	0	0		$ 0
Reconciliation:
Funded status	(1,009)	(1,224)
Accrued pension cost	$ (1,009)	$ (1,224)
Assumptions:
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.