Summary of Significant Accounting Policies - Schedule of Regulatory Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Regulatory Assets
Total Regulatory Assets	$ 87,103		$ 69,020
Regulatory Liabilities
Total Regulatory Liabilities	46,687		48,069
Underrecovered purchased fuel costs
Regulatory Assets
Total Regulatory Assets	6,865		1,651
Under-recovered GRIP Revenue [Member]
Regulatory Assets
Total Regulatory Assets	1,491		0
Deferred post retirement benefits
Regulatory Assets
Total Regulatory Assets	19,762	[1]	8,578	[1]
Deferred transaction and transition costs
Regulatory Assets
Total Regulatory Assets	0		471
Deferred conversion and development costs
Regulatory Assets
Total Regulatory Assets	3,745		1,320
Environmental regulatory assets and expenditures
Regulatory Assets
Total Regulatory Assets	4,452	[1]	5,170	[1]
Acquisition adjustment
Regulatory Assets
Total Regulatory Assets	45,607	[2]	47,478	[2]
Loss on reacquired debt
Regulatory Assets
Total Regulatory Assets	1,372		1,486
Other
Regulatory Assets
Total Regulatory Assets	3,809		2,866
Self insurance
Regulatory Liabilities
Total Regulatory Liabilities	1,003	[3]	1,000	[3]
Overrecovered purchased fuel costs
Regulatory Liabilities
Total Regulatory Liabilities	2,936		2,869
Over-recovered GRIP Revenue [Member]
Regulatory Liabilities
Total Regulatory Liabilities			518
Storm reserve
Regulatory Liabilities
Total Regulatory Liabilities	2,982	[3]	2,875	[3]
Accrued asset removal cost
Regulatory Liabilities
Total Regulatory Liabilities	39,583	[4]	39,510	[4]
Deferred gains
Regulatory Liabilities
Total Regulatory Liabilities	0	[5]	783	[5]
Other
Regulatory Liabilities
Total Regulatory Liabilities	$ 183		$ 514

[1] All of our environmental expenditures incurred to date and current estimate of future environmental expenditures have been approved by various PSCs for recovery. See Note 19, Environmental Commitments and Contingencies, for additional information on our environmental contingencies.

[2] We are allowed to include the premiums paid in various natural gas utility acquisitions in Florida in our rate bases and recover them over a specific time period pursuant to the Florida PSC approvals. Included in these amounts are $1.3 million of the premium paid by FPU, $34.2 million of the premium paid by Chesapeake in 2009, including the gross up of the amount for income tax, because it is not tax deductible, and $746,000 of the premium paid by FPU in 2010.

[3] Pursuant to the Florida PSC order, we were required to defer and amortize, until 2014, certain gains identified during the FPU merger integration.

[4] In accordance with regulatory treatment, our depreciation rates are comprised of two components – historical cost and the estimated cost of removal, net of estimated salvage, of certain regulated properties. We collect these costs in base rates through depreciation expense with a corresponding credit to accumulated depreciation. Because the accumulated estimated removal costs meet the requirements of authoritative guidance related to regulated operations, we have accounted for them as a regulatory liability and have reclassified them from accumulated depreciation to accumulated removal costs in our consolidated balance sheets.

[5] We have self-insurance and storm reserves that allow us to collect through rates amounts to be used against general claims, storm restoration costs and other losses as they are incurred.