Goodwill and Intangible Assets (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Balance at beginning of period	$ 205,143
Gross goodwill		$ 1,072,991
Accumulated Impairment		(867,848)
Current year activity
Balance at end of period	205,143
Civil [Member]
Goodwill [Line Items]
Balance at beginning of period	205,143
Gross goodwill		492,074
Accumulated Impairment		(286,931)
Current year activity
Balance at end of period	205,143
Building [Member]
Goodwill [Line Items]
Balance at beginning of period
Gross goodwill		424,724
Accumulated Impairment		(424,724)
Current year activity
Balance at end of period
Specialty Contractors [Member]
Goodwill [Line Items]
Balance at beginning of period
Gross goodwill		156,193
Accumulated Impairment		$ (156,193)
Current year activity
Balance at end of period