Segment Reporting (Schedule of Assets by Reportable Segments) (Details) - USD ($) $ in Thousands |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Assets by segment [Line Items] | |||
| Total assets | $ 1,961,029 | $ 1,963,829 | $ 1,777,944 |
| Operating Segments [Member] | Data Centers [Member] | |||
| Assets by segment [Line Items] | |||
| Total assets | 1,008,793 | 1,001,357 | 909,477 |
| Operating Segments [Member] | Healthcare [Member] | |||
| Assets by segment [Line Items] | |||
| Total assets | 893,057 | 900,114 | 813,742 |
| All Other [Member] | |||
| Assets by segment [Line Items] | |||
| Total assets | $ 59,179 | $ 62,358 | $ 54,725 |