Segment Information (Information About Industry Segments And Geographic Areas) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues from unrelated entities	$ 1,599,385,000	$ 1,568,401,000
Total revenues	1,599,385,000	1,568,401,000
Operating income (loss)	69,374,000	51,265,000
Restructuring expenses	(909,000)	(1,363,000)
Interest expense	(2,248,000)	(1,862,000)
Interest income	234,000	357,000
Income before income taxes	67,360,000	49,760,000
Total assets	3,407,516,000		3,465,915,000
Insurance recoveries		2,600,000
United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Restructuring expenses	0	0
United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Restructuring expenses	76,000	0
United States Building Services [Member]
Segment Reporting Information [Line Items]
Restructuring expenses	0	(38,000)
United Kingdom Construction And Building Services [Member]
Segment Reporting Information [Line Items]
Restructuring expenses	(685,000)	(1,325,000)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Restructuring expenses	(300,000)	0
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(23,197,000)	(20,609,000)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(15,467,000)	(14,358,000)
Total assets	420,572,000		482,388,000
UNITED STATES
Segment Reporting Information [Line Items]
Revenues from unrelated entities	1,501,149,000	1,449,401,000
Total revenues	1,501,149,000	1,449,401,000
Operating income (loss)	84,453,000	65,707,000
Total assets	2,826,177,000		2,822,699,000
UNITED STATES | United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	308,136,000	307,584,000
UNITED STATES | United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	513,011,000	541,117,000
UNITED STATES | United States Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	448,044,000	455,156,000
UNITED STATES | United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	231,958,000	145,544,000
UNITED STATES | Operating Segments [Member] | United States Electrical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	314,797,000	309,775,000
Operating income (loss)	21,655,000	18,940,000
Total assets	321,182,000		329,742,000
UNITED STATES | Operating Segments [Member] | United States Mechanical Construction And Facilities Services [Member]
Segment Reporting Information [Line Items]
Total revenues	519,111,000	551,784,000
Operating income (loss)	19,106,000	11,140,000
Total assets	767,811,000		795,256,000
UNITED STATES | Operating Segments [Member] | United States Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	457,964,000	462,390,000
Operating income (loss)	20,298,000	12,880,000
Total assets	762,331,000		756,785,000
UNITED STATES | Operating Segments [Member] | United States Industrial Services [Member]
Segment Reporting Information [Line Items]
Total revenues	232,474,000	146,061,000
Operating income (loss)	23,394,000	22,747,000
Total assets	974,853,000		940,916,000
UNITED KINGDOM | United Kingdom Construction And Building Services [Member]
Segment Reporting Information [Line Items]
Revenues from unrelated entities	98,236,000	119,000,000
UNITED KINGDOM | Operating Segments [Member] | United Kingdom Construction And Building Services [Member]
Segment Reporting Information [Line Items]
Total revenues	98,236,000	119,000,000
Operating income (loss)	1,297,000	1,279,000
Total assets	$ 160,767,000		$ 160,828,000