Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Contracts Revenue	$ 1,123,137	$ 1,199,505	$ 3,271,378	$ 3,564,140
State And Local Agencies [Member]
Contracts Revenue	618,357		1,660,072
Federal Agencies [Member]
Contracts Revenue	91,892		262,805
Private Owners [Member]
Contracts Revenue	412,888		1,348,501
Civil [Member]
Contracts Revenue	431,488	395,820	1,097,075	1,172,977
Civil [Member] \| State And Local Agencies [Member]
Contracts Revenue	341,067		894,613
Civil [Member] \| Federal Agencies [Member]
Contracts Revenue	26,944		67,571
Civil [Member] \| Private Owners [Member]
Contracts Revenue	63,477		134,891
Civil [Member] \| Mass Transit [Member]
Contracts Revenue	177,619		485,841
Civil [Member] \| Bridges [Member]
Contracts Revenue	128,240		311,979
Civil [Member] \| Highways [Member]
Contracts Revenue	46,553		129,619
Civil [Member] \| Tunneling [Member]
Contracts Revenue	33,377		66,009
Civil [Member] \| Other [Member]
Contracts Revenue	45,699		103,627
Building [Member]
Contracts Revenue	455,492	493,548	1,392,712	1,483,473
Building [Member] \| State And Local Agencies [Member]
Contracts Revenue	177,377		452,918
Building [Member] \| Federal Agencies [Member]
Contracts Revenue	52,890		149,464
Building [Member] \| Private Owners [Member]
Contracts Revenue	225,225		790,330
Building [Member] \| Health Care Facilities [Member]
Contracts Revenue	127,219		320,416
Building [Member] \| Commercial And Industrial Facilities [Member]
Contracts Revenue	57,505		290,571
Building [Member] \| Hospitality And Gaming [Member]
Contracts Revenue	65,744		226,999
Building [Member] \| Municipal And Government [Member]
Contracts Revenue	67,003		187,984
Building [Member] \| Mixed Use [Member]
Contracts Revenue	40,758		121,348
Building [Member] \| Education Facilities [Member]
Contracts Revenue	43,405		108,763
Building [Member] \| Other [Member]
Contracts Revenue	53,858		136,631
Specialty Contractors [Member]
Contracts Revenue	236,157	$ 310,137	781,591	$ 907,690
Specialty Contractors [Member] \| State And Local Agencies [Member]
Contracts Revenue	99,913		312,541
Specialty Contractors [Member] \| Federal Agencies [Member]
Contracts Revenue	12,058		45,770
Specialty Contractors [Member] \| Private Owners [Member]
Contracts Revenue	124,186		423,280
Specialty Contractors [Member] \| Mass Transit [Member]
Contracts Revenue	63,457		216,808
Specialty Contractors [Member] \| Health Care Facilities [Member]
Contracts Revenue	12,873		43,861
Specialty Contractors [Member] \| Commercial And Industrial Facilities [Member]
Contracts Revenue	48,601		136,892
Specialty Contractors [Member] \| Mixed Use [Member]
Contracts Revenue	37,587		137,420
Specialty Contractors [Member] \| Education Facilities [Member]
Contracts Revenue	26,024		77,626
Specialty Contractors [Member] \| Transportation [Member]
Contracts Revenue	17,150		73,154
Specialty Contractors [Member] \| Condominiums [Member]
Contracts Revenue	18,254		64,104
Specialty Contractors [Member] \| Other [Member]
Contracts Revenue	$ 12,211		$ 31,726