Retirement Plans - Schedule of Multiemployer Plans (Details) (Multiemployer Plan, Plan Information, Available, Domestic, Multiemployer Plans, Pension, USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Multiemployer Plans [Line Items]
Contributions	$ 137,991,000		$ 141,271,000	$ 138,716,000
Plumbers & Pipefitters National Pension Fund
Multiemployer Plans [Line Items]
EIN	526152779
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	10,425,000		12,509,000	10,999,000
Sheet Metal Workers National Pension Fund
Multiemployer Plans [Line Items]
EIN	526112463
Pension Plan Number	001
PPA Zone Status	Yellow		Red
FIP/RP Status	Implemented
Contributions	9,977,000		9,476,000	9,837,000
National Electrical Benefit Fund
Multiemployer Plans [Line Items]
EIN	530181657
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	7,985,000		7,986,000	7,679,000
Central Pension Fund of the International Union of Operating Engineers and Participating Employers
Multiemployer Plans [Line Items]
EIN	366052390
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	6,518,000		6,296,000	6,076,000
Pension, Hospitalization & Benefit Plan of the Electrical Industry- Pension Trust Account
Multiemployer Plans [Line Items]
EIN	136123601
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	6,219,000		6,189,000	5,722,000
National Automatic Sprinkler Industry Pension Fund
Multiemployer Plans [Line Items]
EIN	526054620
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	6,000,000		4,226,000	4,952,000
Plumbers Pipefitters & Mechanical Equipment Service Local Union 392 Pension Plan
Multiemployer Plans [Line Items]
EIN	310655223
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	4,962,000		4,128,000	3,848,000
Electrical Contractors Association of the City of Chicago Local Union 134, IBEW Joint Pension Trust of Chicago Pension Plan 2
Multiemployer Plans [Line Items]
EIN	516030753
Pension Plan Number	002
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	4,051,000		2,412,000	2,179,000
U.A. Local 393 Pension Trust Fund Defined Benefit
Multiemployer Plans [Line Items]
EIN	946359772
Pension Plan Number	002
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	3,585,000		2,811,000	2,181,000
Sheet Metal Workers Pension Plan of Northern California
Multiemployer Plans [Line Items]
EIN	516115939
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	3,467,000		3,658,000	3,881,000
Northern California Pipe Trades Pension Plan
Multiemployer Plans [Line Items]
EIN	943190386
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	3,270,000		2,258,000	3,582,000
Pipefitters Union Local 537 Pension Fund
Multiemployer Plans [Line Items]
EIN	516030859
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	2,981,000		3,690,000	2,747,000
Electrical Workers Local No. 26 Pension Trust Fund
Multiemployer Plans [Line Items]
EIN	526117919
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	2,880,000		2,878,000	3,049,000
Southern California Pipe Trades Retirement Fund
Multiemployer Plans [Line Items]
EIN	516108443
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	2,863,000		5,498,000	3,443,000
Southern California IBEW-NECA Pension Trust Fund
Multiemployer Plans [Line Items]
EIN	956392774
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	2,776,000		3,215,000	3,266,000
Eighth District Electrical Pension Fund
Multiemployer Plans [Line Items]
EIN	846100393
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	2,695,000		3,005,000	3,890,000
Arizona Pipe Trades Pension Plan
Multiemployer Plans [Line Items]
EIN	866025734
Pension Plan Number	001
PPA Zone Status	Green		Green
FIP/RP Status	NA
Contributions	2,098,000		4,108,000	6,871,000
Heating, Piping & Refrigeration Pension Fund
Multiemployer Plans [Line Items]
EIN	521058013
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	1,877,000		2,139,000	2,078,000
Sheet Metal Workers Pension Plan of Southern California, Arizona & Nevada
Multiemployer Plans [Line Items]
EIN	956052257
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	1,824,000		1,271,000	1,072,000
U.A. Local 38 Defined Benefit Pension Plan
Multiemployer Plans [Line Items]
EIN	943042549
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	1,605,000		1,522,000	927,000
Local No. 697 IBEW and Electrical Industry Pension Fund
Multiemployer Plans [Line Items]
EIN	516133048
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	1,499,000		1,443,000	1,757,000
Boilermaker-Blacksmith National Pension Trust
Multiemployer Plans [Line Items]
EIN	486168020
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	1,177,000		1,828,000	2,996,000
Plumbing & Pipe Fitting Local 219 Pension Fund
Multiemployer Plans [Line Items]
EIN	346682376
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	1,107,000		1,142,000	936,000
Building Trades United Pension Trust Fund
Multiemployer Plans [Line Items]
EIN	516049409
Pension Plan Number	001
PPA Zone Status	Yellow		Yellow
FIP/RP Status	Implemented
Contributions	1,033,000		918,000	1,019,000
Steamfitters Local Union No. 420 Pension Plan
Multiemployer Plans [Line Items]
EIN	232004424
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	862,000		831,000	1,557,000
Plumbers & Pipefitters Local 162 Pension Fund
Multiemployer Plans [Line Items]
EIN	316125999
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented	[1]
Contributions	818,000		770,000	737,000
Local 73 Retirement Plan
Multiemployer Plans [Line Items]
EIN	156016577
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Implemented	[1]
Contributions	805,000		225,000	0
U.A. Local 467 Defined Benefit Plan
Multiemployer Plans [Line Items]
EIN	942353807
Pension Plan Number	005
PPA Zone Status	Red		Red
FIP/RP Status	Implemented
Contributions	787,000		538,000	534,000
Carpenters Pension Trust Fund for Northern California
Multiemployer Plans [Line Items]
EIN	946050970
Pension Plan Number	001
PPA Zone Status	Red		Red
FIP/RP Status	Pending
Contributions	522,000		452,000	539,000
Other Multiemployer Pension Plans
Multiemployer Plans [Line Items]
Contributions	$ 41,323,000		$ 43,849,000	$ 40,362,000

[1] For these respective plans, a funding surcharge was currently in effect for 2014.