Business Segments (Reportable Segments) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Segments
Revenues		$ 1,246,599	$ 1,332,978	$ 1,308,130	$ 1,085,369	$ 1,200,830	$ 1,340,739	$ 1,312,438	$ 1,066,465	$ 4,973,076	$ 4,920,472	$ 4,492,309
Income from construction operations		52,050	$ 60,919	$ 48,829	$ 40,122	15,474	$ 38,974	$ 30,881	$ 20,084	201,920	105,413	241,690
Capital Expenditures										15,743	35,912	75,013
Depreciation and amortization	[1]									67,302	41,634	53,702
Assets		4,038,620				3,861,300				4,038,620	3,861,300
External and Intersegment Customers [Member]
Business Segments
Revenues										5,211,876	5,133,715	4,590,227
Intersegment Elimination [Member]
Business Segments
Revenues										(238,800)	(213,243)	(97,918)
Corporate Cash And Cash Equivalents [Member]
Business Segments
Assets	[2]	155,329				383,510				155,329	383,510
Civil [Member]
Business Segments
Revenues										1,668,963	1,889,907	1,687,144
Income from construction operations										172,668	145,213	220,554
Capital Expenditures										13,541	8,383	65,377
Depreciation and amortization	[1]									48,561	22,601	31,674
Assets		2,152,123				1,957,991				2,152,123	1,957,991
Civil [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues										1,830,857	2,005,193	1,730,468
Civil [Member] | Intersegment Elimination [Member]
Business Segments
Revenues										(161,894)	(115,286)	(43,324)
Building [Member]
Business Segments
Revenues										2,069,841	1,802,535	1,503,837
Income from construction operations										51,564	(1,240)	24,697
Capital Expenditures										516	2,877	735
Depreciation and amortization	[1]									2,186	2,728	3,466
Assets		917,317				711,201				917,317	711,201
Building [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues										2,146,747	1,900,492	1,558,431
Building [Member] | Intersegment Elimination [Member]
Business Segments
Revenues										(76,906)	(97,957)	(54,594)
Specialty Contractors [Member]
Business Segments
Revenues										1,234,272	1,228,030	1,301,328
Income from construction operations										37,908	15,682	50,998
Capital Expenditures										1,005	1,193	6,974
Depreciation and amortization	[1]									5,035	5,507	12,018
Assets		$ 813,851				$ 808,598				813,851	808,598
Specialty Contractors [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues										1,234,272	1,228,030	1,301,328
Segment [Member]
Business Segments
Revenues										4,973,076	4,920,472	4,492,309
Income from construction operations										262,140	159,655	296,249
Capital Expenditures										15,062	12,453	73,086
Depreciation and amortization	[1]									55,782	30,836	47,158
Segment [Member] | External and Intersegment Customers [Member]
Business Segments
Revenues										5,211,876	5,133,715	4,590,227
Segment [Member] | Intersegment Elimination [Member]
Business Segments
Revenues										(238,800)	(213,243)	(97,918)
Corporate Segment [Member]
Business Segments
Income from construction operations	[3]									(60,220)	(54,242)	(54,559)
Capital Expenditures	[3]									681	23,459	1,927
Depreciation and amortization	[1],[3]									$ 11,520	$ 10,798	$ 6,544

[1] Depreciation and amortization is included in income from construction operations.

[2] Consists principally of cash, equipment, tax-related assets and insurance-related assets, offset by the elimination of assets related to intersegment revenue.

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