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Multiemployer plans (Details 15) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Multiemployer Plans [Line Items] |  |  |  |
Multiemployer plan red zone status funded percentage, maximum | 65.00% |  |  |
Multiemployer plan yellow zone status funded percentage, minimum | 65.00% |  |  |
Mulitiemployer plan yellow status funded percentage, maximum | 80.00% |  |  |
Multiemployer plan green zone status funded percentage, minimum | 80.00% |  |  |
Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Multiemployer plan, period contributions | $ 34,779 |  | $ 29,158 | $ 30,276
Edison Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 936061681 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Green |  | Green |
Multiemployer plans, certified zone status, date | Dec. 31, 2012 |  | Dec. 31, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | No |  |  |
Multiemployer plan, period contributions | 5,171 |  | 2,700 | 1,933
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Dec. 31, 2014 |  |  |
IBEW Local 38 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 346574238 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |
Multiemployer plans, certified zone status, date | Apr. 30, 2012 |  | Apr. 30, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 2,771 |  | 1,469 | 1,277
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Apr. 27, 2014 |  |  |
IBEW Local No. 82 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 316127268 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Red |  | Red |
Multiemployer plans, certified zone status, date | Jun. 30, 2012 |  | Jun. 30, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 1,093 |  | 1,331 | 1,569
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Dec. 01, 2013 |  |  |
IBEW Local 648 Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 316134845 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Red |  | Red |
Multiemployer plans, certified zone status, date | Feb. 29, 2012 |  | Feb. 28, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 564 |  | 722 | 781
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Aug. 31, 2015 |  |  |
Laborers Pension Trust Fund for Northern California [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 946277608 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |
Multiemployer plans, certified zone status, date | May 31, 2012 |  | May 31, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 567 |  | 628 | 413
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Jun. 30, 2012 | [1] |  |
Multiemployer plans, collective-bargaining, date range - initial | Jun. 30, 2011 | [1] |  |
Local Union 212 IBEW Pension Trust Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 316127280 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |
Multiemployer plans, certified zone status, date | Apr. 30, 2012 |  | Apr. 30, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 664 |  | 776 | 679
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Jun. 02, 2013 |  |  |
National Electrical Benefit Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 530181657 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Green |  | Green |
Multiemployer plans, funding improvement plan and rehabilitation plan | No |  |  |
Multiemployer plan, period contributions | 5,603 |  | 4,841 | 4,826
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Dec. 31, 2016 |  |  |
Multiemployer plans, collective-bargaining, date range - initial | Aug. 31, 2011 | [1] |  |
OE Pension Trust Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 946090764 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Yellow |  | Yellow |
Multiemployer plans, certified zone status, date | Dec. 31, 2012 |  | Dec. 31, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 1,156 |  | 1,367 | 1,035
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Mar. 31, 2016 |  |  |
Multiemployer plans, collective-bargaining, date range - initial | Jun. 30, 2010 | [1] |  |
Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 836011320 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Red |  | Red |
Multiemployer plans, certified zone status, date | Dec. 31, 2012 |  | Dec. 31, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 91 |  | 96 | 106
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Oct. 31, 2005 | [1] |  |
Operating Engineers Pension Trust [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number | 956032478 |  |  |
Multiemployer plan number | 001 |  |  |
Multiemployer plans, certified zone status | Red |  | Red |
Multiemployer plans, certified zone status, date | Jun. 30, 2012 |  | Jun. 30, 2011 |
Multiemployer plans, funding improvement plan and rehabilitation plan | Implemented |  |  |
Multiemployer plan, period contributions | 761 |  | 458 | 343
Multiemployer plans, surcharge | No |  |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | Dec. 31, 2016 |  |  |
Multiemployer plans, collective-bargaining, date range - initial | Jun. 30, 2013 |  |  |
Multiemployer Plan, Individually Insignificant Multiemployer Plans [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Multiemployer plan, period contributions | $ 16,338 |  | $ 14,770 | $ 17,314
[1] | Plan includes collective bargaining agreements which have expired. The agreements contain provisions that automatically renew the existing contracts in lieu of a new negotiated collective bargaining agreement.

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- Definition The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1 + Details
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- Definition Mulitiemployer plan yellow status funded percentage, maximum. + References No definition available. + Details
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- Definition Multiemployer plan green zone status funded percentage, minimum. + References No definition available. + Details
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- Definition Multiemployer plan red zone status funded percentage, maximum. + References No definition available. + Details
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- Definition Date expired of the collective bargaining arrangement requiring contributions to the multiemployer plan, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References No definition available. + Details
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- Definition Multiemployer plan yellow zone status funded percentage, minimum. + References No definition available. + Details
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- Definition Three digit plan number for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Amount of contributions made to multiemployer plans by the employer. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450691-114947 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Date of the multiemployer plan's year end to which the certified zone status relates, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan, in CCYY-MM-DD format. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Indicate whether a funding improvement plan or rehabilitation plan has been implemented or is pending for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "pending", "implemented", "other", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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- Definition Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA". + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 5 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947 + Details
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