Employee Benefit Plans - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Jan. 31, 2011	Dec. 31, 2014 plan	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Number of Plans		3
Income tax benefits		$ 3,700,000
Pre-merger regulatory asset		3,633,000
Total unrecognized cost		29,106,000
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		380,000
One-percentage point increase in health care inflation rate, service cost and interest cost components		14,000
One-percentage point decrease in health care inflation rate, accumulated postretirement benefit obligation		302,000
One-percentage point decrease in health care inflation rate, service cost and interest cost components		11,000
Percentage of eligible participants contribution to the plan		100.00%
Maximum percentage of eligible compensation		6.00%
Employer matching contribution vested, percentage		100.00%
Employer matching contribution vested, period		2 years
Employee contribution age		55 years
Deferral rate		3.00%
Deferral rate increase, minimum		1.00%
Deferral rate increase, maximum		6.00%
Assets Held-in-trust		3,700,000	3,100,000
Employer contributions to pension plan		4,100,000	3,700,000	2,900,000
Shares reserved to fund future contributions		855,975
Deferred Compensation Plan		1,300,000	1,100,000
Minimum
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution vested, percentage		20.00%
Employer matching contribution vested, period		1 year
Maximum
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution vested, percentage		100.00%
Employer matching contribution vested, period		2 years
Chesapeake Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		0
Total unrecognized cost		4,410,000
Unfunded accumulated benefit obligation		(2,903,000)	(1,525,000)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		475,000
Expected contribution		642,000
Chesapeake Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Maximum percent of benefit obligation required	110.00%
Chesapeake SERP
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		0
Total unrecognized cost		1,059,000
Unfunded accumulated benefit obligation		(2,650,000)	(2,210,000)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		151,000
Expected contribution		151,000
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		92,000
Unfunded accumulated benefit obligation		(1,238,000)	(1,262,000)
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		79,000
Expected contribution		79,000
FPU Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		46,000	54,000
Total unrecognized cost		279,000
Curtailment gain		892,000
Unfunded accumulated benefit obligation		(1,712,000)	(1,519,000)
Health care inflation rate		5.50%
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		207,000
Expected contribution		207,000
FPU Medical Plan | Unregulated operations
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain, unregulated operations		170,000
FPU Medical Plan | Regulated liability
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain, regulatory liability		722,000
Amortization of Curtailment Gain Regulatory Liability		212,000	510,000
FPU Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Pre-merger regulatory asset		3,587,000	4,300,000
Total unrecognized cost		23,266,000
Unfunded accumulated benefit obligation		(23,096,000)	(11,539,000)
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		1,600,000
Expected contribution		$ 2,957,000