Employee Benefit Plans - Additional Information (Detail) $ in Thousands		12 Months Ended
		Dec. 31, 2018 USD ($) plan shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans | plan		3
Income tax benefits		$ 2,100
Pre-merger regulatory asset		557
Total unrecognized cost		23,500
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%
Maximum percentage of eligible compensation		6.00%
Employer matching contribution vested, percentage		100.00%
Deferred Compensation Arrangement with Individual, Requisite Service Period		2 years
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		$ 5,500	$ 5,000	$ 4,500
Shares reserved to fund future contributions | shares		831,183
Investments, Fair Value Disclosure		$ 6,711	6,756
Deferred compensation obligation		$ 3,854	3,395
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		10.00%
Number Of Years to Collect Benefits		15 years
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		$ 0
Total unrecognized cost		3,865
Unfunded accumulated benefit obligation		(2,063)	(2,093)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		163
Expected contribution	[1]	528
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Merger Related Costs Allowed To Be Recovered In Future Rates		500
Defined Benefit Plan, Amortization of Transition Asset (Obligation)			1,300
Pre-merger regulatory asset		543
Total unrecognized cost		19,087
Unfunded accumulated benefit obligation		(15,776)	(16,268)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		1,200
Expected contribution	[1]	3,091
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		0
Total unrecognized cost		559
Unfunded accumulated benefit obligation		(2,285)	(2,428)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		383
Expected contribution	[2]	$ 383
Medical
Defined Benefit Plan Disclosure [Line Items]
Health care inflation rate		5.00%
Chesapeake Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		$ 0
Total unrecognized cost		54
Unfunded accumulated benefit obligation		$ (1,002)	(1,128)
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		$ 96
Expected contribution	[2]	96
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		14	22
Total unrecognized cost		(65)
Unfunded accumulated benefit obligation		$ (1,187)	(1,287)
Health care inflation rate		5.00%
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 94
Expected contribution	[2]	94
Rabbi Trust Associated With Deferred Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure		$ 6,689	$ 6,734
FPU Medical Plan and Chesapeake OPRB [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans		2

[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.