Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 1,183,284	$ 1,123,137	$ 1,120,085	$ 1,028,156	$ 1,193,068	$ 1,199,505	$ 1,247,274	$ 1,117,361	$ 4,454,662	$ 4,757,208	$ 4,973,076
State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									2,318,545
Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									350,647
Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,785,470
Civil
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,586,093	1,602,175	1,668,963
Civil | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,294,630
Civil | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									95,567
Civil | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									195,896
Civil | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									702,614
Civil | Bridges [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									431,202
Civil | Highways [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									202,423
Civil | Tunneling [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									103,980
Civil | Products And Services Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									145,874
Building
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,861,699	1,941,325	2,069,841
Building | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									617,133
Building | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									201,745
Building | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,042,821
Building | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									67,588
Building | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									428,819
Building | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									374,312
Building | Hospitality And Gaming [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									301,871
Building | Municipal And Government [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									261,496
Building | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									150,549
Building | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									145,147
Building | Products And Services Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									131,917
Specialty Contractors
Disaggregation of Revenue [Line Items]
Contracts Revenue									1,006,870	$ 1,213,708	$ 1,234,272
Specialty Contractors | State And Local Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									406,782
Specialty Contractors | Federal Agencies [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									53,335
Specialty Contractors | Private Owners [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									546,753
Specialty Contractors | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									296,092
Specialty Contractors | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									52,392
Specialty Contractors | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									189,632
Specialty Contractors | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									163,308
Specialty Contractors | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									99,214
Specialty Contractors | Transportation [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									83,551
Specialty Contractors | Multi-Unit Residential [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									81,023
Specialty Contractors | Products And Services Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue									$ 41,658