Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 1,207,595	$ 1,250,729
State and local agencies
Disaggregation of Revenue [Line Items]
Revenue	610,007	674,934
Federal agencies
Disaggregation of Revenue [Line Items]
Revenue	123,231	78,390
Private owners
Disaggregation of Revenue [Line Items]
Revenue	474,357	497,405
Civil
Disaggregation of Revenue [Line Items]
Revenue	475,575	486,629
Civil | State and local agencies
Disaggregation of Revenue [Line Items]
Revenue	390,502	396,045
Civil | Federal agencies
Disaggregation of Revenue [Line Items]
Revenue	51,633	36,661
Civil | Private owners
Disaggregation of Revenue [Line Items]
Revenue	33,440	53,923
Civil | Mass Transit
Disaggregation of Revenue [Line Items]
Revenue	308,875	297,143
Civil | Military Defense Facilities
Disaggregation of Revenue [Line Items]
Revenue	49,536	23,610
Civil | Bridges
Disaggregation of Revenue [Line Items]
Revenue	46,167	52,184
Civil | Water
Disaggregation of Revenue [Line Items]
Revenue	26,810	23,744
Civil | Highways
Disaggregation of Revenue [Line Items]
Revenue	11,326	32,582
Civil | Other
Disaggregation of Revenue [Line Items]
Revenue	32,861	57,366
Building
Disaggregation of Revenue [Line Items]
Revenue	407,233	481,764
Building | State and local agencies
Disaggregation of Revenue [Line Items]
Revenue	76,581	146,016
Building | Federal agencies
Disaggregation of Revenue [Line Items]
Revenue	50,361	31,973
Building | Private owners
Disaggregation of Revenue [Line Items]
Revenue	280,291	303,775
Building | Mass Transit
Disaggregation of Revenue [Line Items]
Revenue	26,535	57,847
Building | Other
Disaggregation of Revenue [Line Items]
Revenue	9,895	24,896
Building | Commercial And Industrial Facilities
Disaggregation of Revenue [Line Items]
Revenue	130,052	133,049
Building | Hospitality And Gaming
Disaggregation of Revenue [Line Items]
Revenue	100,567	118,987
Building | Municipal And Government
Disaggregation of Revenue [Line Items]
Revenue	71,909	69,502
Building | Education Facilities
Disaggregation of Revenue [Line Items]
Revenue	38,317	31,622
Building | Mixed Use
Disaggregation of Revenue [Line Items]
Revenue	19,549	9,972
Building | Health Care Facilities
Disaggregation of Revenue [Line Items]
Revenue	10,409	35,889
Specialty Contractors
Disaggregation of Revenue [Line Items]
Revenue	324,787	282,336
Specialty Contractors | State and local agencies
Disaggregation of Revenue [Line Items]
Revenue	142,924	132,873
Specialty Contractors | Federal agencies
Disaggregation of Revenue [Line Items]
Revenue	21,237	9,756
Specialty Contractors | Private owners
Disaggregation of Revenue [Line Items]
Revenue	160,626	139,707
Specialty Contractors | Mass Transit
Disaggregation of Revenue [Line Items]
Revenue	181,163	148,671
Specialty Contractors | Water
Disaggregation of Revenue [Line Items]
Revenue	21,154	9,838
Specialty Contractors | Other
Disaggregation of Revenue [Line Items]
Revenue	18,031	13,470
Specialty Contractors | Commercial And Industrial Facilities
Disaggregation of Revenue [Line Items]
Revenue	38,749	53,505
Specialty Contractors | Education Facilities
Disaggregation of Revenue [Line Items]
Revenue	13,356	16,557
Specialty Contractors | Mixed Use
Disaggregation of Revenue [Line Items]
Revenue	9,539	13,802
Specialty Contractors | Multi Unit Residential
Disaggregation of Revenue [Line Items]
Revenue	$ 42,795	$ 26,493