Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 1,125,275	$ 1,120,085	$ 2,083,762	$ 2,148,241
Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	473,658	402,473	807,152	665,587
Civil [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	243,620	158,096	389,870	308,222
Civil [Member] | Bridges [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	86,467	120,929	155,774	183,739
Civil [Member] | Highways [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	60,244	65,809	101,287	83,066
Civil [Member] | Tunneling [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	29,586	23,931	64,526	32,632
Civil [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	53,741	33,708	95,695	57,928
Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	428,318	446,979	861,784	937,220
Building [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	118,564	59,318	227,917	233,066
Building [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	60,796	118,116	141,023	193,197
Building [Member] | Municipal And Government [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	68,580	70,528	130,542	120,981
Building [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	47,062	32,876	89,590	65,358
Building [Member] | Hospitality And Gaming [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	35,939	79,490	83,896	161,255
Building [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	41,211	13,171	70,388	13,171
Building [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	23,582	38,814	60,209	80,590
Building [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	32,584	34,666	58,219	69,602
Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	223,299	270,633	414,826	545,434
Specialty Contractors [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	43,618	48,952	87,641	88,291
Specialty Contractors [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	9,248	14,623	20,899	30,988
Specialty Contractors [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	14,036	26,298	25,616	51,602
Specialty Contractors [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	100,016	78,169	181,411	153,351
Specialty Contractors [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	18,036	51,976	28,705	99,833
Specialty Contractors [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	3,726	22,019	10,161	56,004
Specialty Contractors [Member] | Multi-Unit Residential [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	19,225	22,761	30,614	45,850
Specialty Contractors [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 15,394	$ 5,835	$ 29,779	$ 19,515