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Multiemployer plans (Details 13) - USD ($) | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
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 |  | $ 44,527,000 | $ 39,112,000 | $ 42,817,000
Alaska Laborers-Employers Retirement Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number |  | 916028298 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Yellow | Yellow |
Multiemployer plans, certified zone status, date |  | Jun. 30, 2016 | Jun. 30, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 766,000 | $ 917,000 | 666,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Dec. 31, 2016 |  |
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, 2016 | Dec. 31, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | No |  |
Multiemployer plan, period contributions |  | $ 6,242,000 | $ 5,517,000 | 9,061,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Dec. 31, 2017 |  |
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 |  | Green | Red |
Multiemployer plans, certified zone status, date |  | Jun. 30, 2016 | Jun. 30, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 2,560,000 | $ 2,252,000 | 1,392,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Dec. 01, 2019 |  |
IBEW Local No. 357 Pension Plan A [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number |  | 886023284 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Green | Green |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | No |  |
Multiemployer plan, period contributions |  | $ 3,016,000 | $ 1,896,000 | 3,575,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | May 31, 2018 |  |
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, 2016 | Feb. 28, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 773,000 | $ 745,000 | 1,110,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Sep. 02, 2018 |  |
Idaho Plumbers and Pipefitters Pension Plan [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number |  | 826010346 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Green | Green |
Multiemployer plans, certified zone status, date |  | May 31, 2016 | May 31, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | No |  |
Multiemployer plan, period contributions |  | $ 1,221,000 | $ 1,169,000 | 1,125,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Sep. 30, 2019 |  |
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, 2016 | Apr. 30, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 1,146,000 | $ 937,000 | 568,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Jun. 02, 2019 |  |
National Automatic Sprinkler Industry Pension Fund [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number |  | 526054620 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Red | Red |
Multiemployer plans, certified zone status, date |  | Dec. 31, 2016 | Dec. 31, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 775,000 | $ 677,000 | 608,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date, first |  | Jul. 31, 2018 |  |
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last |  | Mar. 31, 2021 |  |
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 |  | $ 6,366,000 | $ 5,271,000 | 6,476,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date, first |  | Jan. 01, 2017 |  |
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last |  | May 31, 2020 |  |
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 | [1] | 836011320 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Red | Red |
Multiemployer plans, certified zone status, date |  | Dec. 31, 2016 | Dec. 31, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 0 | $ 0 | 68,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date | [2] | Oct. 31, 2005 |  |
Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member] | Withdrawal from Multiemployer Defined Benefit Plan [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Multiemployer discounted future quarterly payments |  | $ 42,000 |  |
Multiemployer withdrawal liability prior accrual |  | 16,400,000 |  |
Multiemployer plans, withdrawal obligation |  | $ 5,200,000 |  |
Sheet Metal Workers Pension Plan of Southern CA, AZ, and NV [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number |  | 956052257 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Red | Red |
Multiemployer plans, certified zone status, date |  | Dec. 31, 2016 | Dec. 31, 2015 |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 1,087,000 | $ 714,000 | 676,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Jun. 30, 2017 |  |
Southwest Marine Pension Trust [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Entity tax identification number |  | 956123404 |  |
Multiemployer plan number |  | 001 |  |
Multiemployer plans, certified zone status |  | Red | Red |
Multiemployer plans, funding improvement plan and rehabilitation plan |  | Implemented |  |
Multiemployer plan, period contributions |  | $ 50,000 | $ 26,000 | 31,000
Multiemployer plans, surcharge |  | No |  |
Multiemployer plans, collective-bargaining arrangement, expiration date |  | Jan. 31, 2019 |  |
Multiemployer Plan, Individually Insignificant Multiemployer Plans [Member] | Multiemployer plans, pension [Member] |  |  |  |
Multiemployer Plans [Line Items] |  |  |  |
Multiemployer plan, period contributions |  | $ 20,525,000 | $ 18,991,000 | $ 17,461,000
[1] | The Company withdrew from the plan as of October 26, 2014, as discussed later.
[2] | 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 Mulitiemployer plan yellow status funded percentage, maximum. + 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 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=65877416&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=65877416&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=65877416&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=65877416&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=65877416&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=65877416&loc=SL14450657-114947 + Details
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- Definition Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire first in a group of associated collective bargaining arrangements, 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=65877416&loc=SL14450657-114947 + Details
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- Definition Expiration date of the collective bargaining arrangement requiring contributions to the multiemployer plan that will expire last in a group of associated collective bargaining arrangements, 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=65877416&loc=SL14450657-114947 + Details
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