Related Party Transactions (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Related Party Transactions | |||
| Repayment of security deposit | $ 0.1 | ||
| Rental income from related entity | $ 0.3 | $ 0.3 | |
| Executive Officer | |||
| Related Party Transactions | |||
| Expenses incurred related to the services received from related party | $ 0.0 | $ 1.4 | $ 1.7 |
| Minimum | |||
| Related Party Transactions | |||
| Ownership interest (as percent) | 5.00% | 5.00% | |