Segment Information (Information About Industry Segments And Geographic Areas) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,933,416	$ 1,652,585	$ 3,678,386	$ 3,241,772
Total revenues	1,933,416	1,652,585	3,678,386	3,241,772
Operating income (loss)	92,289	77,703	147,904	133,033
Restructuring expenses	(641)	(433)	(732)	(441)
Interest expense	(3,118)	(2,208)	(5,494)	(4,424)
Interest income	192	182	357	358
Income from continuing operations before income taxes	89,363	75,677	142,767	128,967
Total assets	3,800,366		3,800,366		$ 3,542,657
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(26,249)	(18,828)	(48,456)	(33,240)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(22,958)	(17,693)	(43,915)	(36,119)
Total assets	487,914		487,914		536,993
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,842,832	1,561,000	3,500,166	3,063,237
Total revenues	1,842,832	1,561,000	3,500,166	3,063,237
Operating income (loss)	112,630	92,995	185,982	164,381
Total assets	3,197,004		3,197,004		2,871,882
UNITED STATES \| United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	420,632	346,202	768,921	665,196
UNITED STATES \| United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	629,895	554,003	1,241,785	1,065,029
UNITED STATES \| United States Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	458,797	435,627	898,448	875,119
UNITED STATES \| United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	333,508	225,168	591,012	457,893
UNITED STATES \| Operating Segments [Member] \| United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	430,101	347,448	784,205	667,686
Operating income (loss)	23,011	25,277	39,718	41,951
Restructuring expenses			0
Total assets	597,231		597,231		372,525
UNITED STATES \| Operating Segments [Member] \| United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	633,118	557,815	1,248,350	1,071,182
Operating income (loss)	38,180	32,364	62,057	53,265
Restructuring expenses			(198)	(6)
Total assets	876,681		876,681		894,366
UNITED STATES \| Operating Segments [Member] \| United States Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	472,110	448,990	924,445	898,718
Operating income (loss)	18,291	17,939	32,193	38,917
Restructuring expenses			(534)	(541)
Total assets	795,623		795,623		721,653
UNITED STATES \| Operating Segments [Member] \| United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Total revenues	333,752	225,575	591,622	458,891
Operating income (loss)	33,148	17,415	52,014	30,248
Total assets	927,469		927,469		883,338
UNITED KINGDOM \| United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	90,584	91,585	178,220	178,535
UNITED KINGDOM \| Operating Segments [Member] \| United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	90,584	91,585	178,220	178,535
Operating income (loss)	3,258	$ 2,834	6,569	$ 5,212
Total assets	$ 115,448		$ 115,448		$ 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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