Intangible Lease Liabilities, Net (Schedule of Estimated Future Amortization Income of Below-Market Leases) (Details) - USD ($) $ in Thousands |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Below Market Lease, Net, Amortization Income, Fiscal Year Maturity [Abstract] | |||
| 2019 | $ 4,927 | ||
| 2020 | 4,871 | ||
| 2021 | 4,843 | ||
| 2022 | 3,752 | ||
| 2023 | 3,091 | ||
| Thereafter | 36,122 | ||
| Total | $ 56,374 | $ 57,606 | $ 61,294 |