Accounts Payable and Other Liabilities (Schedule of Accounts Payable and Other Liabilities) (Details) - USD ($) $ in Thousands |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Payables and Accruals [Abstract] | |||
| Accounts payable and accrued expenses | $ 10,135 | $ 9,188 | $ 13,220 |
| Accrued interest expense | 3,129 | 3,219 | 2,410 |
| Accrued property taxes | 2,299 | 2,309 | 1,532 |
| Distributions payable to stockholders | 7,315 | 7,317 | 6,566 |
| Tenant deposits | 875 | 875 | 682 |
| Deferred rental income | 6,431 | 6,647 | 3,277 |
| Derivative liabilities | 827 | 0 | 22 |
| Total accounts payable and other liabilities | $ 31,011 | $ 29,555 | $ 27,709 |