Segment Information (Information About Industry Segments And Geographic Areas) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,611,881,000	$ 1,606,242,000	$ 1,590,035,000	$ 1,538,521,000	$ 1,517,962,000	$ 1,482,241,000	$ 1,348,013,000	$ 1,265,243,000	$ 6,346,679,000	$ 5,613,459,000	$ 4,851,953,000
Total revenues									6,346,700,000	5,613,500,000	4,852,000,000
Less intersegment revenues									(82,900,000)	(42,600,000)	(38,200,000)
Operating income (loss)									249,967,000	210,793,000	(26,528,000)
Restructuring expenses									(145,000)	(1,240,000)	(1,835,000)
Impairment loss on goodwill and identifiable intangible assets	0	0	0	0	(3,795,000)	0	0	0	0	(3,795,000)	(246,081,000)
Interest expense									(7,275,000)	(11,261,000)	(12,153,000)
Interest income									1,556,000	1,820,000	2,657,000
Gain on sale of equity investment									0	0	7,900,000
Income from continuing operations before income taxes									244,248,000	201,352,000	(28,124,000)
Capital expenditures									37,875,000	29,581,000	19,359,000
Depreciation and amortization of Property, plant and equipment									31,200,000	27,400,000	25,500,000
Costs and estimated earnings in excess of billings on uncompleted contracts	93,061,000				114,836,000				93,061,000	114,836,000	88,253,000
Billings in excess of costs and estimated earnings on uncompleted contracts	383,527,000				441,695,000				383,527,000	441,695,000	456,690,000
Long-lived assets	1,027,000,000				1,038,800,000				1,027,000,000	1,038,800,000	740,500,000
Goodwill	566,588,000				566,805,000				566,588,000	566,805,000	406,804,000
Total assets	3,107,070,000				3,014,076,000				3,107,070,000	3,014,076,000	2,755,542,000
United States electrical construction and facilities services segment
Segment Reporting Information [Line Items]
Revenues from unrelated entities									1,211,700,000	1,155,100,000	1,158,900,000
Total revenues									1,233,500,000	1,161,800,000	1,167,800,000
Operating income (loss)									100,700,000	84,600,000	70,400,000
Capital expenditures									3,300,000	2,600,000	3,500,000
Depreciation and amortization of Property, plant and equipment									3,900,000	4,100,000	4,400,000
Costs and estimated earnings in excess of billings on uncompleted contracts	28,200,000				35,800,000				28,200,000	35,800,000	25,700,000
Billings in excess of costs and estimated earnings on uncompleted contracts	89,900,000				130,700,000				89,900,000	130,700,000	161,500,000
Long-lived assets	14,200,000				15,000,000				14,200,000	15,000,000	16,500,000
Goodwill	3,823,000				3,823,000				3,823,000	3,823,000	3,823,000
Total assets	284,000,000				277,300,000				284,000,000	277,300,000	295,100,000
United States Mechanical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									2,296,400,000	1,917,400,000	1,720,200,000
Total revenues									2,324,200,000	1,925,400,000	1,727,200,000
Operating income (loss)									123,500,000	116,000,000	132,000,000
Capital expenditures									7,600,000	6,500,000	2,500,000
Depreciation and amortization of Property, plant and equipment									6,200,000	4,700,000	4,600,000
Costs and estimated earnings in excess of billings on uncompleted contracts	32,000,000				36,100,000				32,000,000	36,100,000	21,000,000
Billings in excess of costs and estimated earnings on uncompleted contracts	217,900,000				242,100,000				217,900,000	242,100,000	196,000,000
Long-lived assets	268,300,000				259,700,000				268,300,000	259,700,000	214,500,000
Goodwill	201,150,000				199,126,000				201,150,000	199,126,000	175,865,000
Total assets	751,600,000				727,500,000				751,600,000	727,500,000	580,400,000
United States Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									2,299,800,000	2,012,000,000	1,510,500,000
Total revenues									2,333,100,000	2,039,900,000	1,532,800,000
Operating income (loss)									82,300,000	69,100,000	59,300,000
Capital expenditures									22,700,000	16,400,000	11,900,000
Depreciation and amortization of Property, plant and equipment									17,700,000	16,100,000	14,000,000
Costs and estimated earnings in excess of billings on uncompleted contracts	17,600,000				28,400,000				17,600,000	28,400,000	21,200,000
Billings in excess of costs and estimated earnings on uncompleted contracts	38,300,000				33,400,000				38,300,000	33,400,000	32,400,000
Long-lived assets	731,500,000				754,000,000				731,500,000	754,000,000	500,200,000
Goodwill	361,615,000				363,856,000				361,615,000	363,856,000	227,116,000
Total assets	1,234,000,000				1,237,100,000				1,234,000,000	1,237,100,000	862,900,000
Total United States Operations
Segment Reporting Information [Line Items]
Revenues from unrelated entities									5,807,900,000	5,084,500,000	4,389,600,000
Total revenues									5,807,900,000	5,084,500,000	4,389,600,000
Operating income (loss)									306,500,000	269,700,000	261,700,000
Capital expenditures									33,600,000	25,500,000	17,900,000
Depreciation and amortization of Property, plant and equipment									27,800,000	24,900,000	23,000,000
Costs and estimated earnings in excess of billings on uncompleted contracts	77,800,000				100,300,000				77,800,000	100,300,000	67,900,000
Billings in excess of costs and estimated earnings on uncompleted contracts	346,100,000				406,200,000				346,100,000	406,200,000	389,900,000
Long-lived assets	1,014,000,000				1,028,700,000				1,014,000,000	1,028,700,000	731,200,000
Goodwill	566,600,000				566,800,000				566,600,000	566,800,000	406,800,000
Total assets	2,269,600,000				2,241,900,000				2,269,600,000	2,241,900,000	1,738,400,000
Canada Construction
Segment Reporting Information [Line Items]
Capital expenditures									0	100,000	200,000
Depreciation and amortization of Property, plant and equipment									0	300,000	600,000
Costs and estimated earnings in excess of billings on uncompleted contracts	0				0				0	0	12,000,000
Billings in excess of costs and estimated earnings on uncompleted contracts	0				0				0	0	16,200,000
Long-lived assets	0				0				0	0	3,500,000
Goodwill	0				0				0	0	0
Total assets	0				0				0	0	103,000,000
United Kingdom Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									538,800,000	529,000,000	462,400,000
Total revenues									538,800,000	529,000,000	462,400,000
Operating income (loss)									7,100,000	9,200,000	15,700,000
Capital expenditures									3,600,000	3,300,000	1,000,000
Depreciation and amortization of Property, plant and equipment									2,600,000	1,500,000	1,100,000
Costs and estimated earnings in excess of billings on uncompleted contracts	15,300,000				14,500,000				15,300,000	14,500,000	8,400,000
Billings in excess of costs and estimated earnings on uncompleted contracts	37,400,000				35,500,000				37,400,000	35,500,000	50,600,000
Long-lived assets	11,500,000				8,600,000				11,500,000	8,600,000	4,300,000
Goodwill	0				0				0	0	0
Total assets	214,500,000				227,000,000				214,500,000	227,000,000	201,600,000
Other International Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									0	0	0
Total revenues									0	0	0
Operating income (loss)									0	0	(100,000)
Capital expenditures									0	0	0
Depreciation and amortization of Property, plant and equipment									0	0	0
Costs and estimated earnings in excess of billings on uncompleted contracts	0				0				0	0	0
Billings in excess of costs and estimated earnings on uncompleted contracts	0				0				0	0	0
Long-lived assets	0				0				0	0	0
Goodwill	0				0				0	0	0
Total assets	0				0				0	0	0
Corporate Administration
Segment Reporting Information [Line Items]
Operating income (loss)									(63,500,000)	(63,100,000)	(55,900,000)
Capital expenditures									700,000	700,000	300,000
Depreciation and amortization of Property, plant and equipment									800,000	700,000	800,000
Long-lived assets	1,500,000				1,500,000				1,500,000	1,500,000	1,500,000
Goodwill	0				0				0	0	0
Total assets	$ 623,000,000				$ 545,200,000				$ 623,000,000	$ 545,200,000	$ 712,500,000