Derivative Instruments and Hedging Activities (Schedule of Offsetting of Derivative Liabilities) (Details) - USD ($) $ in Thousands |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Derivative Instruments and Hedging Activities Disclosure [Abstract] | |||
| Gross Amounts of Recognized Liabilities | $ 827 | $ 0 | $ 22 |
| Gross Amounts Offset in the Balance Sheet | 0 | 0 | 0 |
| Net Amounts of Liabilities Presented in the Balance Sheet | 827 | 0 | 22 |
| Gross Amounts Not Offset in the Balance Sheet, Financial Instruments Collateral | (84) | 0 | 0 |
| Gross Amounts Not Offset in the Balance Sheet, Cash Collateral | 0 | 0 | 0 |
| Net Amount | $ 743 | $ 0 | $ 22 |