Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 1,250,729	$ 958,487
State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	674,934	498,864
Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	78,390	71,078
Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	497,405	388,545
Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	486,629	333,494
Civil [Member] | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	396,045	257,107
Civil [Member] | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	36,661	23,158
Civil [Member] | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	53,923	53,229
Civil [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	297,143	146,250
Civil [Member] | Bridges [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	52,184	69,307
Civil [Member] | Tunneling [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	25,955	34,940
Civil [Member] | Highways [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	32,582	41,043
Civil [Member] | Water [Member
Disaggregation of Revenue [Line Items]
Contracts Revenue	23,744	9,668
Civil [Member] | Military Defense Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	23,610	10,281
Civil [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	31,411	22,005
Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	481,764	433,466
Building [Member] | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	146,016	144,686
Building [Member] | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	31,973	40,151
Building [Member] | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	303,775	248,629
Building [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	57,847	29,177
Building [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	133,049	109,353
Building [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	35,889	80,227
Building [Member] | Hospitality And Gaming [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	118,987	69,310
Building [Member] | Municipal And Government [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	69,502	61,962
Building [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	9,972	15,274
Building [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	31,622	42,528
Building [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	24,896	25,635
Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	282,336	191,527
Specialty Contractors [Member] | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	132,873	97,071
Specialty Contractors [Member] | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	9,756	7,769
Specialty Contractors [Member] | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	139,707	86,687
Specialty Contractors [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	148,671	81,394
Specialty Contractors [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	53,505	44,023
Specialty Contractors [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	2,522	11,652
Specialty Contractors [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	13,802	10,669
Specialty Contractors [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	16,557	11,580
Specialty Contractors [Member] | Multi-Unit Residential [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	26,493	11,389
Specialty Contractors [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 20,786	$ 20,820