Summary of Significant Account Policies, Restricted Cash (Table) (Details) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|---|---|---|---|
| RESTRICTED CASH AND CASH EQUIVALENTS [ABSTRACT] | ||||||
| Cash and cash equivalents | $ 132,925 | $ 127,632 | $ 114,198 | $ 135,992 | $ 163,412 | $ 247,556 |
| Restricted cash | 10,056 | 6,558 | 5,040 | 5,386 | $ 13,480 | |
| Total cash and cash equivalents and restricted cash | $ 142,981 | $ 134,190 | $ 119,238 | $ 141,377 |