Segment Information (Information About Industry Segments And Geographic Areas) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,589,187us-gaap_SalesRevenueNet	$ 1,590,539us-gaap_SalesRevenueNet
Total revenues	1,589,187us-gaap_Revenues	1,590,539us-gaap_Revenues
Operating income (loss)	55,330us-gaap_OperatingIncomeLoss	72,124us-gaap_OperatingIncomeLoss
Restructuring expenses	(8)us-gaap_RestructuringCharges	(225)us-gaap_RestructuringCharges
Interest expense	(2,216)us-gaap_InterestExpense	(2,248)us-gaap_InterestExpense
Interest income	176us-gaap_InvestmentIncomeInterest	234us-gaap_InvestmentIncomeInterest
Income from continuing operations before income taxes	53,290	70,110
Total assets	3,315,582us-gaap_Assets		3,388,967us-gaap_Assets
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(14,412)	(23,197)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(18,426)	(15,467)
Restructuring expenses	0	(300)
Total assets	389,277		442,321
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,502,237	1,501,149
Total revenues	1,502,237	1,501,149
Operating income (loss)	71,386	84,453
Total assets	2,793,836		2,816,306
UNITED STATES \| United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	318,994	308,136
UNITED STATES \| United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	511,026	513,011
UNITED STATES \| United States Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	439,492	448,044
UNITED STATES \| United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	232,725	231,958
UNITED STATES \| Operating Segments [Member] \| United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	320,238	314,797
Operating income (loss)	16,674	21,655
Restructuring expenses	(2)	0
Total assets	338,325		332,150
UNITED STATES \| Operating Segments [Member] \| United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	513,367	519,111
Operating income (loss)	20,901	19,106
Restructuring expenses	(6)
Total assets	777,328		793,056
UNITED STATES \| Operating Segments [Member] \| United States Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	449,728	457,964
Operating income (loss)	20,978	20,298
Total assets	745,226		737,082
UNITED STATES \| Operating Segments [Member] \| United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Total revenues	233,316	232,474
Operating income (loss)	12,833	23,394
Total assets	932,957		954,018
UNITED KINGDOM \| United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	86,950	89,390
UNITED KINGDOM \| Operating Segments [Member] \| United Kingdom Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	86,950	89,390
Operating income (loss)	2,378	3,363
Total assets	$ 132,469		$ 130,340

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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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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