Revenue (Disaggregation Of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 958,487	$ 1,028,156
Civil [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	333,494	263,114
Civil [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	146,250	150,126
Civil [Member] | Bridges [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	69,307	62,811
Civil [Member] | Highways [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	41,043	17,257
Civil [Member] | Tunneling [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	34,940	8,701
Civil [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	41,954	24,219
Building [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	433,466	490,241
Building [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	109,353	173,747
Building [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	80,227	75,081
Building [Member] | Municipal And Government [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	61,962	50,452
Building [Member] | Hospitality And Gaming [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	47,957	81,765
Building [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	42,528	32,482
Building [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	36,627	41,777
Building [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	29,177
Building [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	25,635	34,937
Specialty Contractors [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	191,527	274,801
Specialty Contractors [Member] | Commercial And Industrial Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	44,023	39,339
Specialty Contractors [Member] | Health Care Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	11,652	16,365
Specialty Contractors [Member] | Education Facilities [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	11,580	25,304
Specialty Contractors [Member] | Mixed Use [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	10,669	47,857
Specialty Contractors [Member] | Mass Transit [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	81,394	75,182
Specialty Contractors [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	6,435	33,985
Specialty Contractors [Member] | Multi-Unit Residential [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	11,389	23,089
Specialty Contractors [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Contracts Revenue	$ 14,385	$ 13,680