Annual report pursuant to Section 13 and 15(d)

Construction Contract and Other Service Revenues (Narrative) (Details)

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Construction Contract and Other Service Revenues (Narrative) (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Construction contract revenue | Revenue from Contract with Customer Benchmark | Concentration risk | United States Government      
Concentration Risk [Line Items]      
Percentage of revenue 74.00% 95.00% 98.00%