Accumulated Other Comprehensive Income (Schedule of Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2019 |
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] | ||||||||||||
| Interest and other expense, net | $ 9,835 | $ 9,476 | $ 8,938 | $ 8,208 | $ 7,741 | $ 6,932 | $ 6,786 | $ 5,073 | $ 3,764 | $ 34,364 | $ 22,555 | $ 4,390 |
| Interest Rate Swaps [Member] | Unrealized Income on Derivative Instruments [Member] | Amounts Reclassified from Accumulated Other Comprehensive Income to Net Income [Member] | ||||||||||||
| Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] | ||||||||||||
| Interest and other expense, net | $ (656) | $ 129 | $ (818) | $ 1,386 | $ 96 | |||||||