| Shareholders' Equity and Capital Stock - o/s RSUs (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | |
|---|---|---|---|
| Sep. 30, 2018 | Sep. 30, 2018 | Dec. 31, 2017 | |
| RSUs | |||
| Number of unvested units | 1,296,227 | 1,296,227 | 1,175,952 | 
| Remaining life (years) | 10 months 21 days | ||
| Aggregate Intrinsic Value | $ 1,050 | ||
| August 22. 2018 | |||
| RSUs | |||
| Number of unvested units | 239,423 | 239,423 | |
| Remaining life (years) | 1 year 10 months 21 days | ||
| Aggregate Intrinsic Value | $ 194 | ||
| December 16, 2016 | |||
| RSUs | |||
| Number of unvested units | 570,578 | 570,578 | |
| Remaining life (years) | 2 months 16 days | ||
| Aggregate Intrinsic Value | $ 462 | ||
| December 15, 2017 | |||
| RSUs | |||
| Number of unvested units | 486,226 | 486,226 | |
| Remaining life (years) | 1 year 2 months 16 days | ||
| Aggregate Intrinsic Value | $ 394 | 
| X | ||||||||||
| 
- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
| 
- Details 
 |