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Operations and Significant Accounting Policies - Concentraion of Credit Risk (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Customer Information [Line Items] |  |  |
Major Customer, Percent of Total Revenue | 12.00% | 12.30% | 12.60%
Large Power Customer [Member] |  |  |
Customer Information [Line Items] |  |  |
Number of Customers | 9 |  |
Large Power Customers, Accounts Receivable | $ 14.2 | $ 13.7 |

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- Definition For unclassified balance sheet, amounts due from customers or clients for goods or services that have been delivered or sold in the normal course of business. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.9) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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