Employee Benefit Plans - Additional Information (Detail) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017	Dec. 31, 2017 USD ($)	Dec. 31, 2017 plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans						2		3
Income tax benefits							$ 3,100
Pre-merger regulatory asset							1,326
Total unrecognized cost							23,347
Expected Amortization Of Pre Merger Regulatory Asset			$ 0
One-percentage point increase in health care inflation rate, accumulated postretirement benefit obligation			277
One-percentage point increase in health care inflation rate, service cost and interest cost components			11
One-percentage point decrease in health care inflation rate, accumulated postretirement benefit obligation			215
One-percentage point decrease in health care inflation rate, service cost and interest cost components			$ 8
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
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			$ 5,000	$ 4,500	$ 4,100
Shares reserved to fund future contributions | shares			831,183
Investments, Fair Value Disclosure				4,902			6,756
Deferred compensation obligation				2,416			3,395
Minimum
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of eligible compensation			3.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
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							3,629
Unfunded accumulated benefit obligation				(2,687)			(2,093)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year							359
Expected contribution	[1]						687
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Merger Related Costs Allowed To Be Recovered In Future Rates							1,300
Defined Benefit Plan, Amortization of Transition Asset (Obligation)				2,100
Pre-merger regulatory asset							1,304
Total unrecognized cost							18,787
Unfunded accumulated benefit obligation				(20,560)			(16,268)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year							1,500
Expected contribution	[1]						3,078
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset							0
Total unrecognized cost							733
Unfunded accumulated benefit obligation				(2,428)			(2,428)
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year							151
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]
Pre-merger regulatory asset							0
Total unrecognized cost							166
Unfunded accumulated benefit obligation				(1,132)			(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							97
Expected contribution	[2]						97
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset				30			22
Total unrecognized cost							32
Unfunded accumulated benefit obligation				(1,349)			(1,287)
Health care inflation rate						5.00%
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year							88
Expected contribution	[2]						88
Rabbi Trust Associated With Deferred Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure				$ 4,881			$ 6,734
Subsequent Event
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of eligible compensation		10.00%

[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.