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Summary of Significant Accounting Policies - Significant Estimates Used by Management in Determining Fair Values of Company's Reporting Units (Detail)
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12 Months Ended | ||
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Electric Power and Natural Gas and Pipeline Services [Member]
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| Segment Reporting Information [Line Items] | |||
| Years of cash flows before terminal value | 5 years | 5 years | 5 years |
| Weighting of three approaches: | |||
| Discounted cash flows | 70.00% | 70.00% | 70.00% |
| Market multiple | 15.00% | 15.00% | 15.00% |
| Market capitalization | 15.00% | 15.00% | 15.00% |
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Electric Power and Natural Gas and Pipeline Services [Member] | Minimum [Member]
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| Segment Reporting Information [Line Items] | |||
| Discount rates | 12.00% | 13.00% | 15.00% |
| EBITDA multiples | 4.5 | 4.5 | 4.5 |
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Electric Power and Natural Gas and Pipeline Services [Member] | Maximum [Member]
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| Segment Reporting Information [Line Items] | |||
| Discount rates | 13.00% | 13.00% | 15.00% |
| EBITDA multiples | 8.0 | 8.0 | 8.0 |
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Fiber Optic Licensing [Member]
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| Segment Reporting Information [Line Items] | |||
| Years of cash flows before terminal value | 15 years | 15 years | 15 years |
| Weighting of three approaches: | |||
| Discounted cash flows | 90.00% | 90.00% | 90.00% |
| Market multiple | 5.00% | 5.00% | 5.00% |
| Market capitalization | 5.00% | 5.00% | 5.00% |
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Fiber Optic Licensing [Member] | Minimum [Member]
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| Segment Reporting Information [Line Items] | |||
| Discount rates | 12.00% | 14.00% | 14.00% |
| EBITDA multiples | 9.5 | 9.5 | 9.5 |
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Fiber Optic Licensing [Member] | Maximum [Member]
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| Segment Reporting Information [Line Items] | |||
| Discount rates | 12.00% | 14.00% | 14.00% |
| EBITDA multiples | 9.5 | 9.5 | 9.5 |