Multiemployer plans (Details 13) - USD ($)		12 Months Ended
		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.