Significant Segment Financial Data (Detail) - USD ($)
$ in Millions |
3 Months Ended |
6 Months Ended |
|
Jun. 30, 2016 |
Jun. 30, 2015 |
Jun. 30, 2016 |
Jun. 30, 2015 |
Dec. 31, 2015 |
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |
|
|
|
|
|
| Revenues |
$ 74.5
|
$ 77.5
|
$ 200.3
|
$ 249.7
|
|
| Segment Profit |
2.5
|
1.7
|
13.4
|
15.3
|
|
| Capital Expenditures |
28.3
|
25.3
|
39.6
|
38.4
|
|
| Segment Assets |
1,051.7
|
993.9
|
1,051.7
|
993.9
|
$ 1,038.8
|
| Gas Segment |
|
|
|
|
|
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |
|
|
|
|
|
| Revenues |
28.9
|
27.6
|
102.0
|
127.9
|
|
| Segment Profit |
|
(0.7)
|
9.4
|
10.9
|
|
| Capital Expenditures |
18.8
|
15.6
|
21.9
|
22.8
|
|
| Segment Assets |
593.8
|
573.8
|
593.8
|
573.8
|
590.9
|
| Electricity |
|
|
|
|
|
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |
|
|
|
|
|
| Revenues |
44.1
|
48.4
|
95.2
|
118.7
|
|
| Segment Profit |
2.1
|
1.9
|
3.4
|
3.7
|
|
| Capital Expenditures |
7.3
|
7.3
|
13.0
|
11.7
|
|
| Segment Assets |
419.4
|
406.5
|
419.4
|
406.5
|
415.1
|
| All Other Segments |
|
|
|
|
|
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |
|
|
|
|
|
| Segment Profit |
0.1
|
0.2
|
|
0.1
|
|
| Capital Expenditures |
2.2
|
2.3
|
4.7
|
3.8
|
|
| Segment Assets |
31.5
|
7.6
|
31.5
|
7.6
|
26.3
|
| Unregulated Operation |
|
|
|
|
|
| Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] |
|
|
|
|
|
| Revenues |
1.5
|
1.5
|
3.1
|
3.1
|
|
| Segment Profit |
0.3
|
0.3
|
0.6
|
0.6
|
|
| Capital Expenditures |
|
0.1
|
|
0.1
|
|
| Segment Assets |
$ 7.0
|
$ 6.0
|
$ 7.0
|
$ 6.0
|
$ 6.5
|