Segment Information (Information About Industry Segments And Geographic Areas) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,923,174	$ 1,699,128	$ 5,601,560	$ 4,940,900
Total revenues	1,923,174	1,699,128	5,601,560	4,940,900
Operating income (loss)	86,064	69,966	233,968	202,999
Restructuring expenses	(539)	(301)	(1,271)	(742)
Interest expense	(3,479)	(2,226)	(8,973)	(6,650)
Interest income	161	157	518	515
Income from continuing operations before income taxes	82,746	67,897	225,513	196,864
Total assets	3,894,953		3,894,953		$ 3,542,657
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(26,482)	(23,286)	(74,938)	(56,526)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(23,516)	(15,912)	(67,431)	(52,031)
Total assets	555,508		555,508		536,993
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,850,138	1,602,127	5,350,304	4,665,364
Total revenues	1,850,138	1,602,127	5,350,304	4,665,364
Operating income (loss)	107,528	82,821	293,510	247,202
Total assets	3,230,609		3,230,609		2,871,882
UNITED STATES \| United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	458,553	344,389	1,227,474	1,009,585
UNITED STATES \| United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	697,733	587,522	1,939,518	1,652,551
UNITED STATES \| United States Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	454,800	428,270	1,353,248	1,303,389
UNITED STATES \| United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	239,052	241,946	830,064	699,839
UNITED STATES \| Operating Segments [Member] \| United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	465,476	348,327	1,249,681	1,016,013
Operating income (loss)	30,927	25,528	70,645	67,479
Restructuring expenses			0
Total assets	623,446		623,446		372,525
UNITED STATES \| Operating Segments [Member] \| United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	702,464	592,077	1,950,814	1,663,259
Operating income (loss)	39,447	26,926	101,504	80,191
Restructuring expenses			(401)	(6)
Total assets	929,994		929,994		894,366
UNITED STATES \| Operating Segments [Member] \| United States Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	469,191	442,674	1,393,636	1,341,392
Operating income (loss)	22,568	16,027	54,761	54,944
Restructuring expenses			(870)	(842)
Total assets	778,507		778,507		721,653
UNITED STATES \| Operating Segments [Member] \| United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Total revenues	239,489	242,335	831,111	701,226
Operating income (loss)	14,586	14,340	66,600	44,588
Total assets	898,662		898,662		883,338
UNITED KINGDOM \| United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	73,036	97,001	251,256	275,536
UNITED KINGDOM \| Operating Segments [Member] \| United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	73,036	97,001	251,256	275,536
Operating income (loss)	2,591	$ 3,358	9,160	$ 8,570
Total assets	$ 108,836		$ 108,836		$ 133,782

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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