Business Segments (Narrative) (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2017 USD ($) segment $ / shares	Sep. 30, 2016 USD ($) contract $ / shares
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Income from construction operations	$ 49,072	$ 60,919	$ 120,134	$ 149,870
DILUTED EARNINGS PER COMMON SHARE (in dollars per share) | $ / shares	$ 0.47	$ 0.57	$ 1.33	$ 1.32
Building [Member]
Segment Reporting Information [Line Items]
Income from construction operations	$ 14,058	$ 13,296	$ 25,035	$ 38,969
Civil [Member]
Segment Reporting Information [Line Items]
Income from construction operations	38,144	50,307	128,176	129,028
Specialty Contractors [Member]
Segment Reporting Information [Line Items]
Income from construction operations	14,575	11,084	15,330	25,910
Corporate [Member]
Segment Reporting Information [Line Items]
Income from construction operations	$ (17,705)	$ (13,768)	$ (48,407)	(44,037)
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