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Significant Segment Financial Data (Detail) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | $ 126.0 | $ 125.8 |
Segment Profit (Loss) | 12.4 | 10.9 |
Identifiable Segment Assets | 1,134.4 | 1,052.9 | $ 1,128.2
Capital Expenditures | 17.5 | 11.3 |
Gas Segment |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | 74.8 | 73.1 |
Segment Profit (Loss) | 9.9 | 9.4 |
Identifiable Segment Assets | 641.8 | 596.9 | 645.2
Capital Expenditures | 5.7 | 3.1 |
Electric |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | 49.5 | 51.1 |
Segment Profit (Loss) | 2.1 | 1.3 |
Identifiable Segment Assets | 442.8 | 420.8 | 441.1
Capital Expenditures | 8.3 | 5.7 |
All Other Segments |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Segment Profit (Loss) |  | (0.1) |
Identifiable Segment Assets | 42.8 | 28.4 | 35.1
Capital Expenditures | 3.5 | 2.5 |
Unregulated Operation |  |  |
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |  |  |
Revenues | 1.7 | 1.6 |
Segment Profit (Loss) | 0.4 | 0.3 |
Identifiable Segment Assets | $ 7.0 | $ 6.8 | $ 6.8

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