Revenue (Schedule of Revenue by Contract Type) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 1,189,345	$ 1,123,137	$ 3,273,107	$ 3,271,378
Fixed Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	729,433	558,575	1,915,943	1,659,982
Guaranteed Maximum Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	164,261	290,814	571,242	864,499
Unit Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	170,368	159,794	418,745	383,473
Cost Plus Fee And Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	125,283	113,954	367,177	363,424
Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	524,546	431,488	1,331,698	1,097,075
Civil [Member] | Fixed Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	376,230	272,996	969,041	716,826
Civil [Member] | Guaranteed Maximum Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	639	3,025	4,517	11,200
Civil [Member] | Unit Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	142,253	141,917	343,416	332,118
Civil [Member] | Cost Plus Fee And Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	5,424	13,550	14,724	36,931
Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	415,346	455,492	1,277,130	1,392,712
Building [Member] | Fixed Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	144,514	91,972	395,123	267,630
Building [Member] | Guaranteed Maximum Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	159,217	269,069	551,399	801,537
Building [Member] | Unit Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	2,922	9,938	10,950	29,526
Building [Member] | Cost Plus Fee And Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	108,693	84,513	319,658	294,019
Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	249,453	236,157	664,279	781,591
Specialty Contractors [Member] | Fixed Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	208,689	193,607	551,779	675,526
Specialty Contractors [Member] | Guaranteed Maximum Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	4,405	18,720	15,326	51,762
Specialty Contractors [Member] | Unit Price [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	25,193	7,939	64,379	21,829
Specialty Contractors [Member] | Cost Plus Fee And Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	11,166	15,891	32,795	32,474
State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	701,136	618,357	1,829,491	1,660,072
State And Local Agencies [Member] | Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	420,839	341,067	1,059,384	894,613
State And Local Agencies [Member] | Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	144,106	177,377	422,590	452,918
State And Local Agencies [Member] | Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	136,191	99,913	347,517	312,541
Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	413,681	412,888	1,223,874	1,348,501
Private Owners [Member] | Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	70,855	63,477	189,325	134,891
Private Owners [Member] | Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	234,350	225,225	733,103	790,330
Private Owners [Member] | Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	108,476	124,186	301,446	423,280
Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	74,528	91,892	219,742	262,805
Federal Agencies [Member] | Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	32,852	26,944	82,989	67,571
Federal Agencies [Member] | Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	36,890	52,890	121,437	149,464
Federal Agencies [Member] | Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 4,786	$ 12,058	$ 15,316	$ 45,770