Employee Benefit Plans - Additional Information (Detail) $ in Thousands		12 Months Ended
		Dec. 31, 2020 USD ($) plan shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans | plan		3
Income tax benefits		$ 1,800
Total unrecognized cost		23,956
Expected Amortization Of Pre Merger Regulatory Asset		$ 0
Required period of service for eligibility		3 months
Percentage of eligible participants contribution to the plan		100.00%
Employer matching contribution vested, percentage		100.00%
Deferred Compensation Arrangement with Individual, Requisite Service Period		2 years
Deferred Pension Settlement Expense		$ 700
Defined Benefit Plan, Benefit Obligation			2
Employee contribution age		55 years
Deferral rate		80.00%
Deferred Compensation Employer Matching Contribution Rate		6.00%
Number Of Years to Collect Benefits		20 years
Deferral rate increase, minimum		1.00%
Employer contributions to pension plan		$ 5,900	$ 5,700	$ 5,500
Shares reserved to fund future contributions | shares		813,230
Investments, Fair Value Disclosure		$ 10,776	9,229
Deferred compensation obligation		$ 5,679	4,543
Minimum
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of eligible compensation		3.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of eligible compensation		6.00%		10.00%
Number Of Years to Collect Benefits		15 years
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized cost		$ 2,033
Unfunded accumulated benefit obligation		(1,537)	(1,584)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		300
Expected contribution	[1]	384
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized cost		21,242
Unfunded accumulated benefit obligation		(14,400)	(15,601)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		2,100
Expected contribution	[1]	3,409
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized cost		699
Unfunded accumulated benefit obligation		(2,212)	(2,157)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		200
Expected contribution	[2]	$ 151
Medical
Defined Benefit Plan Disclosure [Line Items]
Health care inflation rate		5.00%
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized cost		$ 176
Unfunded accumulated benefit obligation		$ (1,033)	(1,100)
Expected Amortization Of Pre Merger Regulatory Asset			0	$ 0
Health care inflation rate		6.00%
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 100
Expected contribution	[2]	68
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Total unrecognized cost		194
Unfunded accumulated benefit obligation		$ (1,009)	(1,224)
Health care inflation rate		5.00%
Expected contribution	[2]	$ 67
Rabbi Trust Associated With Deferred Compensation [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure		$ 10,755	9,202
FPU Medical Plan and Chesapeake OPRB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans		2
Rabbi Trust Associated With Deferred Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation obligation		$ 10,800	9,200
Deferred Compensation Equity		$ 5,700	$ 4,500

[1] The pension plan is funded; therefore, benefit payments are expected to be paid out of the plan assets.

[2] Benefit payments are expected to be paid out of our general funds.