Derivative Instruments and Hedging Activities (Schedule of Offsetting of Derivative Assets) (Details) - USD ($) $ in Thousands |
Mar. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Derivative Instruments and Hedging Activities Disclosure [Abstract] | |||
| Gross Amounts of Recognized Assets | $ 3,420 | $ 6,204 | $ 3,934 |
| Gross Amounts Offset in the Balance Sheet | 0 | 0 | 0 |
| Net Amounts of Assets Presented in the Balance Sheet | 3,420 | 6,204 | 3,934 |
| 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 | $ 3,336 | $ 6,204 | $ 3,934 |