Summary of Significant Accounting Policies - Revenue (Details) |
6 Months Ended |
|---|---|
Jun. 30, 2016 | |
| Minimum | |
| Revenue Recognition and Deferred Revenue | |
| Period to derive revenue under long-term contracts | 10 years |
| Maximum | |
| Revenue Recognition and Deferred Revenue | |
| Period to derive revenue under long-term contracts | 15 years |