Business Segments (Reconciliation of Segment Results to Consolidated Income Before Income Taxes) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Income from construction operations		$ 90,680	$ 47,306	$ 54,815	$ (925)	$ 59,343	$ 49,072	$ 34,045	$ 37,017	$ 191,876		$ 179,477	$ 201,920
Other income, net										4,256		43,882	6,977
Interest expense										(63,519)		(69,384)	(59,782)
INCOME BEFORE INCOME TAXES		75,152	$ 32,804	$ 39,867	$ (15,210)	45,193	$ 34,396	$ 52,516	$ 21,870	132,613		153,975	149,115
Assets		4,387,752				4,264,123				4,387,752		4,264,123
Reportable Segments [Member]
Income from construction operations										255,625	[1]	245,344	262,140	[2]
Civil
Income from construction operations										168,256	[1]	192,207	172,668	[2]
Assets		2,574,326				2,452,108				2,574,326		2,452,108
Building
Income from construction operations										43,939	[1]	34,199	51,564	[2]
Assets		913,746				909,207				913,746		909,207
Specialty Contractors
Income from construction operations										43,430	[1]	18,938	37,908	[2]
Assets		745,313				767,807				745,313		767,807
Corporate [Member]
Income from construction operations	[3]									(63,749)	[1]	(65,867)	$ (60,220)	[2]
Assets	[4]	$ 154,367				$ 135,001				$ 154,367		$ 135,001

[1] During the year ended December 31, 2018, the Company recorded a charge of $17.8 million in income from construction operations (an after-tax impact of $12.8 million, or $0.25 per diluted share), which was primarily non-cash, as a result of the unexpected outcome of an arbitration decision related to a subcontract back charge dispute on a Civil segment project in New York that was completed in 2013.

[2] During the year ended December 31, 2016 the Company recorded net favorable adjustments totaling $3.0 million in income from construction operations (an after-tax impact of $1.8 million, or $0.04 per diluted share) for various Five Star Electric projects in New York in the Specialty Contractors segment. The net impact included material adjustments related to two electrical subcontract projects: a favorable adjustment of $14.0 million for a completed project (an after-tax impact of $8.2 million, or $0.17 per diluted share) and an unfavorable adjustment of $13.8 million for a project that was nearly complete (an after-tax impact of $8.1 million, or $0.16 per diluted share).

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

[4] As of December 31,(in thousands)20182017Civil$ 2,574,326$ 2,452,108Building 913,746 909,207Specialty Contractors 745,313 767,807Corporate and other(a) 154,367 135,001Total assets$ 4,387,752$ 4,264,123Consists principally of cash, equipment, tax-related assets and insurance-related assets, offset by the elimination of assets related to intersegment revenue.