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Significant Segment Financial Data (Detail) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2015
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | $ 125.8 | $ 172.2 |
Segment Profit | 10.9 | 13.6 |
Identifiable Segment Assets | 1,052.9 | 1,035.1 | $ 1,038.8
Capital Expenditures | 11.3 | 13.0 |
Gas Segment |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | 73.1 | 100.3 |
Segment Profit | 9.4 | 11.6 |
Identifiable Segment Assets | 596.9 | 590.4 | 590.9
Capital Expenditures | 3.1 | 7.2 |
Electricity |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | 51.1 | 70.3 |
Segment Profit | 1.3 | 1.8 |
Identifiable Segment Assets | 420.8 | 418.6 | 415.1
Capital Expenditures | 5.7 | 4.4 |
All Other Segments |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Segment Profit | (0.1) | (0.1) |
Identifiable Segment Assets | 28.4 | 20.5 | 26.3
Capital Expenditures | 2.5 | 1.4 |
Unregulated Operation |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | 1.6 | 1.6 |
Segment Profit | 0.3 | 0.3 |
Identifiable Segment Assets | $ 6.8 | $ 5.6 | $ 6.5

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