Summary of Significant Accounting Policies - Schedule of Regulatory Assets and Liabilities (Detail) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets
Total Regulatory Assets		$ 85,787	$ 87,103
Regulatory Liabilities
Total Regulatory Liabilities		50,429	46,687
Underrecovered purchased fuel costs
Regulatory Assets
Total Regulatory Assets	[1]	4,598	6,865
Under-recovered GRIP Revenue [Member]
Regulatory Assets
Total Regulatory Assets	[1]	3,091	1,491
Deferred post retirement benefits
Regulatory Assets
Total Regulatory Assets	[2]	19,479	19,762
Deferred conversion and development costs
Regulatory Assets
Total Regulatory Assets	[1]	5,729	3,745
Environmental regulatory assets and expenditures
Regulatory Assets
Total Regulatory Assets	[3]	4,158	4,452
Acquisition adjustment
Regulatory Assets
Total Regulatory Assets	[4]	43,735	45,607
Loss on reacquired debt
Regulatory Assets
Total Regulatory Assets	[5]	1,259	1,372
Other
Regulatory Assets
Total Regulatory Assets		3,738	3,809
Self insurance
Regulatory Liabilities
Total Regulatory Liabilities	[6]	1,031	1,003
Overrecovered purchased fuel costs
Regulatory Liabilities
Total Regulatory Liabilities	[1]	6,994	2,936
Storm reserve
Regulatory Liabilities
Total Regulatory Liabilities	[6]	2,973	2,982
Accrued asset removal cost
Regulatory Liabilities
Total Regulatory Liabilities	[7]	39,206	39,583
Other
Regulatory Liabilities
Total Regulatory Liabilities		$ 225	$ 183

[1] We are allowed to recover the asset or are required to pay the liability in rates. We do not earn an overall rate of return on these assets.

[2] The Florida PSC allowed FPU to treat as a regulatory asset the portion of the unrecognized costs pursuant to ASC Topic 715, Compensation - Retirement Benefits, related to its regulated operations. See Note 16, Employee Benefit Plans, for additional information.

[3] 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 us 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.

[4] All of our environmental expenditures incurred to date and our 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.

[5] Gains and losses resulting from the reacquisition of long-term debt are amortized over future periods as adjustments to interest expense in accordance with established regulatory practice.

[6] 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.

[7] In accordance with typical regulatory policy, 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.