Employee Benefit Plans - Additional Information (Detail) $ in Thousands		1 Months Ended	12 Months Ended
		Jan. 31, 2011	Dec. 31, 2015 USD ($) plan shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans | plan			3
Income tax benefits			$ 3,700
Pre-merger regulatory asset			2,864
Total unrecognized cost			28,711
Escrow deposit percent		125.00%
Expected Amortization Of Pre Merger Regulatory Asset			0
One-percentage point increase in health care inflation rate, accumulated postretirement benefit obligation			335
One-percentage point increase in health care inflation rate, service cost and interest cost components			13
One-percentage point decrease in health care inflation rate, accumulated postretirement benefit obligation			268
One-percentage point decrease in health care inflation rate, service cost and interest cost components			$ 10
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%
Deferral rate increase, minimum			1.00%
Employer contributions to pension plan			$ 4,100	$ 4,100	$ 3,700
Shares reserved to fund future contributions | shares			843,037
Investments, Fair Value Disclosure			$ 3,644	3,678
Deferred Compensation Equity			$ (1,883)	(1,258)
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
Number Of Years to Collect Benefits			2 years
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			4,434
Unfunded accumulated benefit obligation			(2,749)	(2,903)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year			505
Expected contribution	[1]		591
Chesapeake Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Maximum percent of benefit obligation required		110.00%
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amortization of Transition Obligations (Assets)			2,800	3,600
Pre-merger regulatory asset			2,826
Total unrecognized cost			23,236
Unfunded accumulated benefit obligation			(22,228)	(23,096)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year			1,600
Expected contribution	[1]		2,980
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset			0
Total unrecognized cost			866
Unfunded accumulated benefit obligation			(2,510)	(2,650)
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			38
Unfunded accumulated benefit obligation			$ (1,153)	(1,238)
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			$ 82
Expected contribution	[2]		82
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset			38	46
Total unrecognized cost			137
Unfunded accumulated benefit obligation			$ (1,444)	$ (1,712)
Health care inflation rate			5.00%
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year			$ 149
Expected contribution	[2]		$ 149

[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.