Annual report pursuant to Section 13 and 15(d)

Construction Contract and Other Service Revenues (Percentage of Revenue - Narrative) (Details)

v3.20.4
Construction Contract and Other Service Revenues (Percentage of Revenue - Narrative) (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Construction contract revenue | Revenue from Contract with Customer Benchmark | Concentration risk | United States Government      
Concentration Risk [Line Items]      
Percentage of revenue 55.00% 74.00% 95.00%