Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 1,177,725	$ 1,189,345	$ 1,125,275	$ 958,487	$ 1,183,284	$ 1,123,137	$ 1,120,085	$ 1,028,156	$ 4,450,832	$ 4,454,662	$ 4,757,208
State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									2,470,245	2,318,545
Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									281,662	350,647
Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,698,925	1,785,470
Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,779,352	1,586,093	1,602,175
Civil [Member] | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,401,001	1,294,630
Civil [Member] | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									116,869	95,567
Civil [Member] | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									261,482	195,896
Civil [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									992,755	702,614
Civil [Member] | Bridges [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									334,117	431,202
Civil [Member] | Tunneling [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									128,229	103,980
Civil [Member] | Highways [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									86,747	202,423
Civil [Member] | Products And Services Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									237,504	145,874
Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,742,040	1,861,699	1,941,325
Building [Member] | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									573,049	617,133
Building [Member] | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									153,467	201,745
Building [Member] | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,015,524	1,042,821
Building [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									201,400	67,588
Building [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									239,299	428,819
Building [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									459,806	374,312
Building [Member] | Hospitality And Gaming [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									297,700	301,871
Building [Member] | Municipal And Government [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									254,736	261,496
Building [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									31,685	150,549
Building [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									143,382	145,147
Building [Member] | Products And Services Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									114,032	131,917
Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									929,440	1,006,870	$ 1,213,708
Specialty Contractors [Member] | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									496,195	406,782
Specialty Contractors [Member] | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									11,326	53,335
Specialty Contractors [Member] | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									421,919	546,753
Specialty Contractors [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									419,402	296,092
Specialty Contractors [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									29,519	52,392
Specialty Contractors [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									186,819	189,632
Specialty Contractors [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									64,302	163,308
Specialty Contractors [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									70,229	99,214
Specialty Contractors [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									7,756	83,551
Specialty Contractors [Member] | Multi-Unit Residential [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									83,903	81,023
Specialty Contractors [Member] | Products And Services Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									$ 67,510	$ 41,658