Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Significant Customers (Details)

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Summary of Significant Accounting Policies - Significant Customers (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
California      
Segment Reporting Information [Line Items]      
Percentage of revenues under contracts or subcontracts 11.00% 13.00% 18.00%
NEW YORK      
Segment Reporting Information [Line Items]      
Percentage of revenues under contracts or subcontracts 15.00%    
Texas      
Segment Reporting Information [Line Items]      
Percentage of revenues under contracts or subcontracts   10.00% 12.00%