Segment Information (Information About Industry Segments And Geographic Areas) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,714,796,000	$ 1,566,711,000	$ 1,552,919,000	$ 1,590,539,000	$ 1,649,279,000	$ 1,605,315,000	$ 1,532,628,000	$ 1,546,305,000	$ 6,424,965,000	$ 6,333,527,000	$ 6,195,494,000
Total revenues									6,424,965,000	6,333,527,000	6,195,494,000
Operating income (loss)									289,878,000	240,350,000	260,303,000
Restructuring expenses									(1,168,000)	(647,000)	(145,000)
Impairment loss on identifiable intangible assets	1,471,000	0	0	0	0	0	0	0	1,471,000	0	0
Gain on sale of building	0	11,749,000	0	0	0	0	0	0	11,749,000	0	0
Interest expense									(9,075,000)	(8,769,000)	(7,275,000)
Interest income									842,000	1,128,000	1,556,000
Income from continuing operations before income taxes									281,645,000	232,709,000	254,584,000
Capital expenditures									38,035,000	35,497,000	37,875,000
Depreciation and amortization of Property, plant and equipment									36,524,000	36,310,000	31,204,000
Costs and estimated earnings in excess of billings on uncompleted contracts	103,201,000				90,727,000				103,201,000	90,727,000	93,061,000
Billings in excess of costs and estimated earnings on uncompleted contracts	368,555,000				381,295,000				368,555,000	381,295,000	383,527,000
Long-lived assets	1,458,340,000				1,499,736,000				1,458,340,000	1,499,736,000	1,026,968,000
Total assets	3,388,967,000				3,465,915,000				3,388,967,000	3,465,915,000	3,107,070,000
Income from reduction in estimate of certain accrued contract costs									4,800,000
Insurance recoveries										2,600,000
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities									6,074,521,000	5,989,975,000	5,807,900,000
Total revenues									6,074,521,000	5,989,975,000	5,807,900,000
Operating income (loss)									334,335,000	297,867,000	306,528,000
Capital expenditures									35,030,000	32,890,000	33,602,000
Depreciation and amortization of Property, plant and equipment									32,336,000	30,989,000	27,838,000
Costs and estimated earnings in excess of billings on uncompleted contracts	94,743,000				82,754,000				94,743,000	82,754,000	77,819,000
Billings in excess of costs and estimated earnings on uncompleted contracts	353,980,000				356,064,000				353,980,000	356,064,000	346,084,000
Long-lived assets	1,449,418,000				1,489,009,000				1,449,418,000	1,489,009,000	1,013,947,000
Total assets	2,816,306,000				2,822,699,000				2,816,306,000	2,822,699,000	2,269,571,000
UNITED STATES | United States electrical construction and facilities services segment
Segment Reporting Information [Line Items]
Revenues from unrelated entities									1,311,988,000	1,345,750,000	1,211,692,000
UNITED STATES | United States Mechanical Construction And Facilities Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									2,201,212,000	2,329,834,000	2,386,498,000
UNITED STATES | United States Building Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									1,721,341,000	1,794,978,000	1,807,917,000
UNITED STATES | United States Industrial Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									839,980,000	519,413,000	401,793,000
UNITED KINGDOM | United Kingdom Building Services
Segment Reporting Information [Line Items]
Revenues from unrelated entities									350,444,000	343,552,000	387,594,000
Operating Segments [Member] | UNITED STATES | United States electrical construction and facilities services segment
Segment Reporting Information [Line Items]
Total revenues									1,326,547,000	1,371,979,000	1,233,468,000
Operating income (loss)									90,873,000	98,114,000	100,736,000
Restructuring expenses									(638,000)	0
Capital expenditures									6,671,000	6,164,000	3,273,000
Depreciation and amortization of Property, plant and equipment									4,237,000	3,640,000	3,926,000
Costs and estimated earnings in excess of billings on uncompleted contracts	32,464,000				28,988,000				32,464,000	28,988,000	28,207,000
Billings in excess of costs and estimated earnings on uncompleted contracts	114,422,000				118,458,000				114,422,000	118,458,000	89,889,000
Long-lived assets	18,792,000				16,512,000				18,792,000	16,512,000	14,146,000
Total assets	332,150,000				329,742,000				332,150,000	329,742,000	283,997,000
Operating Segments [Member] | UNITED STATES | United States Mechanical Construction And Facilities Services
Segment Reporting Information [Line Items]
Total revenues									2,219,886,000	2,387,072,000	2,414,296,000
Operating income (loss)									114,418,000	93,765,000	125,261,000
Restructuring expenses									(230,000)	(479,000)
Capital expenditures									8,631,000	8,866,000	8,119,000
Depreciation and amortization of Property, plant and equipment									7,600,000	7,280,000	6,768,000
Costs and estimated earnings in excess of billings on uncompleted contracts	43,443,000				38,804,000				43,443,000	38,804,000	34,084,000
Billings in excess of costs and estimated earnings on uncompleted contracts	199,983,000				205,974,000				199,983,000	205,974,000	219,876,000
Long-lived assets	288,161,000				293,790,000				288,161,000	293,790,000	269,990,000
Total assets	793,056,000				795,256,000				793,056,000	795,256,000	785,286,000
Operating Segments [Member] | UNITED STATES | United States Building Services
Segment Reporting Information [Line Items]
Total revenues									1,762,697,000	1,839,129,000	1,837,995,000
Operating income (loss)									65,885,000	67,225,000	43,290,000
Restructuring expenses									0	(168,000)
Capital expenditures									10,589,000	7,579,000	11,086,000
Depreciation and amortization of Property, plant and equipment									10,660,000	11,288,000	10,584,000
Costs and estimated earnings in excess of billings on uncompleted contracts	18,555,000				14,957,000				18,555,000	14,957,000	15,528,000
Billings in excess of costs and estimated earnings on uncompleted contracts	38,059,000				30,827,000				38,059,000	30,827,000	36,319,000
Long-lived assets	392,364,000				406,498,000				392,364,000	406,498,000	449,641,000
Total assets	737,082,000				756,785,000				737,082,000	756,785,000	800,081,000
Operating Segments [Member] | UNITED STATES | United States Industrial Services
Segment Reporting Information [Line Items]
Total revenues									842,040,000	522,417,000	405,002,000
Operating income (loss)									63,159,000	38,763,000	37,241,000
Capital expenditures									9,139,000	10,281,000	11,124,000
Depreciation and amortization of Property, plant and equipment									9,839,000	8,781,000	6,560,000
Costs and estimated earnings in excess of billings on uncompleted contracts	281,000				5,000				281,000	5,000	0
Billings in excess of costs and estimated earnings on uncompleted contracts	1,516,000				805,000				1,516,000	805,000	0
Long-lived assets	750,101,000				772,209,000				750,101,000	772,209,000	280,170,000
Total assets	954,018,000				940,916,000				954,018,000	940,916,000	400,207,000
Operating Segments [Member] | UNITED KINGDOM | United Kingdom Building Services
Segment Reporting Information [Line Items]
Total revenues									350,444,000	343,552,000	387,594,000
Operating income (loss)									15,011,000	13,021,000	17,388,000
Capital expenditures									1,935,000	1,536,000	3,604,000
Depreciation and amortization of Property, plant and equipment									3,305,000	4,477,000	2,594,000
Costs and estimated earnings in excess of billings on uncompleted contracts	8,458,000				7,973,000				8,458,000	7,973,000	15,242,000
Billings in excess of costs and estimated earnings on uncompleted contracts	14,575,000				25,231,000				14,575,000	25,231,000	37,443,000
Long-lived assets	6,899,000				8,831,000				6,899,000	8,831,000	11,502,000
Total assets	130,340,000				160,828,000				130,340,000	160,828,000	214,455,000
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)									(68,578,000)	(69,891,000)	(63,468,000)
Restructuring expenses									(300,000)	0
Capital expenditures									1,070,000	1,071,000	669,000
Depreciation and amortization of Property, plant and equipment									883,000	844,000	772,000
Long-lived assets	2,023,000				1,896,000				2,023,000	1,896,000	1,519,000
Total assets	442,321,000				482,388,000				442,321,000	482,388,000	623,044,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues									$ (76,649,000)	$ (130,622,000)	$ (82,861,000)