Multiemployer plans (Details 14) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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				$ 39,112	$ 42,817	$ 39,260
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, 2015	Dec. 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				No
Multiemployer plan, period contributions				$ 5,517	$ 9,061	6,358
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				Red	Red
Multiemployer plans, certified zone status, date				Jun. 30, 2015	Jun. 30, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 2,252	$ 1,392	1,284
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date	[1]			Nov. 29, 2015
IBEW Local No. 246 Pension Plan [Member] | Multiemployer plans, pension [Member]
Multiemployer Plans [Line Items]
Entity tax identification number				346582842
Multiemployer plan number				001
Multiemployer plans, certified zone status				Yellow	Yellow
Multiemployer plans, certified zone status, date				May 31, 2015	May 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 433	$ 694	1,848
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date				Oct. 31, 2017
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				$ 1,896	$ 3,575	2,348
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. 28, 2015	Feb. 28, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 745	$ 1,110	1,489
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, 2015	May 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				No
Multiemployer plan, period contributions				$ 1,169	$ 1,125	1,121
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date				Sep. 30, 2016
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, 2015	Apr. 30, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 937	$ 568	531
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date				Jun. 05, 2016
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, 2015	Dec. 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 677	$ 608	583
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date, first				Mar. 31, 2016
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last				Jul. 31, 2018
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				$ 5,271	$ 6,476	5,883
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date, first	[1]			Jun. 30, 2015
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last				Nov. 30, 2019
Pension Trust Fund for Operating Engineers [Member] | Multiemployer plans, pension [Member]
Multiemployer Plans [Line Items]
Entity tax identification number				946090764
Multiemployer plan number				001
Multiemployer plans, certified zone status				Red	Red
Multiemployer plans, certified zone status, date				Dec. 31, 2015	Dec. 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 1,997	$ 1,445	1,510
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date, first	[1]			Jun. 15, 2015
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last				Jun. 30, 2016
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	[2]			836011320
Multiemployer plan number				001
Multiemployer plans, certified zone status				Red	Red
Multiemployer plans, certified zone status, date				Dec. 31, 2015	Dec. 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 0	$ 68	76
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date	[1]			Oct. 31, 2005
Multiemployer plan, withdrawal obligation			$ 14,000	$ 16,400	$ 14,000
Operating Engineers Local 800 and WY Contractors Association Pension Plan for WY [Member] | Withdrawal from Multiemployer Defined Benefit Plan [Member]
Multiemployer Plans [Line Items]
Loss contingency, loss in period		$ 2,400	$ 14,000
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, 2015	Dec. 31, 2014
Multiemployer plans, funding improvement plan and rehabilitation plan				Implemented
Multiemployer plan, period contributions				$ 714	$ 676	512
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date				Jun. 30, 2016
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				$ 26	$ 31	42
Multiemployer plans, surcharge				No
Multiemployer plans, collective-bargaining arrangement, expiration date, first	[1]			Jan. 31, 2014
Multiemployer Plans, Collective-Bargaining Arrangement, Expiration Date, Last				Jan. 31, 2019
Multiemployer Plan, Individually Insignificant Multiemployer Plans [Member] | Multiemployer plans, pension [Member]
Multiemployer Plans [Line Items]
Multiemployer plan, period contributions				$ 17,478	$ 15,988	$ 15,675

[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.

[2] The Company withdrew from the plan as of October 26, 2014, as discussed below.