Employee Benefit Plans - Additional Information (Detail) $ in Thousands		12 Months Ended
		Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016	Dec. 31, 2016 USD ($)	Dec. 31, 2016 plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans					2		3
Income tax benefits						$ 3,500
Pre-merger regulatory asset						2,095
Total unrecognized cost						27,246
Expected Amortization Of Pre Merger Regulatory Asset		$ 0
Health care inflation rate		100.00%
One-percentage point increase in health care inflation rate, accumulated postretirement benefit obligation		$ 321
One-percentage point increase in health care inflation rate, service cost and interest cost components		12
One-percentage point decrease in health care inflation rate, accumulated postretirement benefit obligation		257
One-percentage point decrease in health care inflation rate, service cost and interest cost components		$ 10
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		$ 4,500	$ 4,100
Shares reserved to fund future contributions | shares		831,183
Investments, Fair Value Disclosure			3,644			4,902
Deferred compensation obligation			1,883			2,416
Minimum
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage of eligible compensation		3.00%
Employer matching contribution vested, percentage		20.00%
Deferred Compensation Arrangement with Individual, Requisite Service Period		1 year
Maximum
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution vested, percentage		100.00%
Deferred Compensation Arrangement with Individual, Requisite Service Period		2 years
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						4,223
Unfunded accumulated benefit obligation			(2,749)			(2,687)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 323
Expected contribution	[1]					746
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amortization of Transition Obligations (Assets)		2,100	2,800
Pre-merger regulatory asset						2,065
Total unrecognized cost						22,108
Unfunded accumulated benefit obligation			(22,228)			(20,560)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		2,600
Expected contribution	[1]					3,041
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset						0
Total unrecognized cost						757
Unfunded accumulated benefit obligation			(2,510)			(2,428)
Defined Benefit Plans, Estimated Future Employer Contributions in 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						70
Unfunded accumulated benefit obligation			(1,153)			(1,132)
Expected Amortization Of Pre Merger Regulatory Asset			0	$ 0
Health care inflation rate		6.00%
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 83
Expected contribution	[2]					83
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset			38			30
Total unrecognized cost						88
Unfunded accumulated benefit obligation			(1,444)			(1,349)
Health care inflation rate		5.00%
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 129
Expected contribution	[2]					129
Rabbi Trust Associated With Deferred Compensation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Investments, Fair Value Disclosure			$ 3,626			$ 4,881

[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.