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%