Business Segments (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Jun. 30, 2017 USD ($) segment $ / shares	Jun. 30, 2016 USD ($) contract $ / shares
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Income from construction operations	$ 34,045	$ 48,829	$ 71,062	$ 88,951
DILUTED EARNINGS PER COMMON SHARE (in dollars per share) | $ / shares	$ 0.59	$ 0.43	$ 0.86	$ 0.74
Building [Member]
Segment Reporting Information [Line Items]
Income from construction operations	$ 5,736	$ 13,223	$ 10,977	$ 25,673
Civil [Member]
Segment Reporting Information [Line Items]
Income from construction operations	58,144	45,056	90,032	78,721
Specialty Contractors [Member]
Segment Reporting Information [Line Items]
Income from construction operations	(14,007)	5,413	755	14,826
Corporate [Member]
Segment Reporting Information [Line Items]
Income from construction operations	$ (15,828)	$ (14,863)	$ (30,702)	(30,269)
Five Star Electric [Member] | Specialty Contractors [Member] | Scenario Favorable Adjustment [Member]
Segment Reporting Information [Line Items]
Income from construction operations				$ 3,000
DILUTED EARNINGS PER COMMON SHARE (in dollars per share) | $ / shares				$ 0.04
Five Star Electric Subcontract [Member]
Segment Reporting Information [Line Items]
Number of projects | contract				2
Five Star Electric Subcontract [Member] | Scenario Unfavorable Adjustment [Member]
Segment Reporting Information [Line Items]
Income from construction operations				$ 13,800
DILUTED EARNINGS PER COMMON SHARE (in dollars per share) | $ / shares				$ 0.17
Five Star Electric Subcontract [Member] | Scenario Favorable Adjustment [Member]
Segment Reporting Information [Line Items]
Income from construction operations				$ 14,000
DILUTED EARNINGS PER COMMON SHARE (in dollars per share) | $ / shares				$ 0.17