Business Segments (Narrative) (Details) $ / shares in Units, $ in Thousands		3 Months Ended
		Mar. 31, 2019 USD ($) segment $ / shares	Mar. 31, 2018 USD ($) $ / shares
Segment Reporting Information [Line Items]
Number of reportable segments | segment		3
Operating Income (Loss)		$ 22,913	$ (925)	[1]
DILUTED LOSS PER COMMON SHARE | $ / shares		$ (0.01)	$ (0.24)
Building [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		$ 3,133	$ 6,425	[1]
Civil [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		41,745	2,839	[1]
Civil [Member] | Scenario Unfavorable Adjustment [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)			17,800
Income from construction operations			$ 12,800
DILUTED LOSS PER COMMON SHARE | $ / shares			$ 0.25
Specialty Contractors [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)		(7,488)	$ 7,235	[1]
Corporate [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	[2]	$ (14,477)	$ (17,424)	[1]

[1] During the three months ended March 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] Consists primarily of corporate general and administrative expenses.