Goodwill and Intangible Assets (Changes in Carrying Amount of Goodwill) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Goodwill [Line Items]
Gross goodwill as of December 31, 2022		$ 1,072,991
Accumulated impairment as of December 31, 2022		(867,848)
Goodwill [Roll Forward]
Balance at beginning of period	$ 205,143
Current year activity	0
Balance at end of period	205,143
Civil
Goodwill [Line Items]
Gross goodwill as of December 31, 2022		492,074
Accumulated impairment as of December 31, 2022		(286,931)
Goodwill [Roll Forward]
Balance at beginning of period	205,143
Current year activity	0
Balance at end of period	205,143
Building
Goodwill [Line Items]
Gross goodwill as of December 31, 2022		424,724
Accumulated impairment as of December 31, 2022		(424,724)
Goodwill [Roll Forward]
Balance at beginning of period	0
Current year activity	0
Balance at end of period	0
Specialty Contractors
Goodwill [Line Items]
Gross goodwill as of December 31, 2022		156,193
Accumulated impairment as of December 31, 2022		$ (156,193)
Goodwill [Roll Forward]
Balance at beginning of period	0
Current year activity	0
Balance at end of period	$ 0