Derivative Instruments and Hedging Activities (Schedule of Income and Losses Recognized on Derivative Instruments) (Details) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|
Mar. 31, 2019 |
Mar. 31, 2018 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Derivative Instruments, Gain (Loss) [Line Items] | |||||
| Amount of Income (Loss) Recognized in OCI on Derivative | $ (2,955) | $ 4,446 | $ 3,208 | $ 1,484 | $ 744 |
| Amount of Income (Loss) Reclassified From Accumulated Other Comprehensive Income to Net Income | 656 | (129) | 818 | (1,386) | (96) |
| Interest Rate Swaps [Member] | |||||
| Derivative Instruments, Gain (Loss) [Line Items] | |||||
| Amount of Income (Loss) Recognized in OCI on Derivative | (2,955) | 4,446 | 3,208 | 1,484 | 744 |
| Interest Rate Swaps [Member] | Interest and Other Expense, Net [Member] | |||||
| Derivative Instruments, Gain (Loss) [Line Items] | |||||
| Amount of Income (Loss) Reclassified From Accumulated Other Comprehensive Income to Net Income | $ 656 | $ (129) | $ 818 | $ (1,386) | $ (96) |