Summary of Significant Accounting Policies - Significant Customers (Details) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| California | |||
| Segment Reporting Information [Line Items] | |||
| Percentage of revenues under contracts or subcontracts | 18.00% | 21.00% | 3.00% |
| Florida | |||
| Segment Reporting Information [Line Items] | |||
| Percentage of revenues under contracts or subcontracts | 14.00% | ||
| Texas | |||
| Segment Reporting Information [Line Items] | |||
| Percentage of revenues under contracts or subcontracts | 12.00% | 13.00% | 22.00% |