Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Reportable segment information
Revenues	$ 1,250,689		$ 1,030,388		$ 3,290,432		$ 3,076,381
Income from construction operations:
Income from construction operations	70,354		58,094		177,294		133,647
Total Assets	3,835,520				3,835,520				3,397,438
Elimination of intersegment revenues [Member]
Reportable segment information
Revenues	(21,789)		(26,054)		(72,333)		(122,765)
Corporate [Member]
Income from construction operations:
Income from construction operations	(13,365)	[1]	(13,624)	[1]	(38,719)	[1]	(36,274)	[1]
Total Assets	602,490	[2]			602,490	[2]			615,108	[2]
Operating segment [Member]
Reportable segment information
Revenues	1,272,478		1,056,442		3,362,765		3,199,146
Income from construction operations:
Income from construction operations	83,719		71,718		216,013		169,921
Total Assets	3,233,030				3,233,030				2,782,330
Civil [Member]
Reportable segment information
Revenues	482,670		397,706		1,238,365		997,864
Civil [Member] | Elimination of intersegment revenues [Member]
Reportable segment information
Revenues	(13,472)		(4,270)		(32,292)		(66,073)
Civil [Member] | Operating segment [Member]
Reportable segment information
Revenues	496,142		401,976		1,270,657		1,063,937
Income from construction operations:
Income from construction operations	53,684		49,559		156,031		104,483
Total Assets	1,764,712				1,764,712				1,384,937
Building [Member]
Reportable segment information
Revenues	412,087		345,049		1,082,031		1,204,983
Building [Member] | Elimination of intersegment revenues [Member]
Reportable segment information
Revenues	(8,317)		(21,784)		(40,041)		(56,682)
Building [Member] | Operating segment [Member]
Reportable segment information
Revenues	420,404		366,833		1,122,072		1,261,665
Income from construction operations:
Income from construction operations	19,159		12,847		28,656		20,855
Total Assets	665,267				665,267				663,314
Specialty Contractors [Member]
Reportable segment information
Revenues	355,932		287,633		970,036		873,534
Specialty Contractors [Member] | Elimination of intersegment revenues [Member]
Reportable segment information
Revenues							(10)
Specialty Contractors [Member] | Operating segment [Member]
Reportable segment information
Revenues	355,932		287,633		970,036		873,544
Income from construction operations:
Income from construction operations	10,876		9,312		31,326		44,583
Total Assets	$ 803,051				$ 803,051				$ 734,079

[1] Consists primarily of corporate general and administrative expenses.

[2] Consists principally of Cash and Cash Equivalents and corporate transportation equipment.